The first time it happened, well, Harry thought it was all a dream. A logical conclusion really, seeing as the last thing he remembered was falling asleep in his bed in Gryffindor Tower, and next thing he was awake on the cold hard ground, surrounded by armor clad strangers pointing swords at him.
Harry looked at them a mo, confused, and more than a little annoyed waking up in danger. Not that he wasn't used to it if course, you know, being who he was, but he was still allowed to be annoyed about it.
In any case, given the surroundings, this was probably, most likely a dream, and since it was a dream, Harry had no obligation to stick around and be poked at by sharp swords, so, thinking back to that funny feeling he got in fourth form when he was trying to hide from Dudley and ended up on the roof of his primary School with little more than a pop, and a dizzy nauseous feeling, Harry willed his dream self to pop out of the predicament he'd been in, directly into another.
He didn't know what it said about his subconscious that his dreams were so bloody and full of fighting. Maybe the incident last week with Quirrelmort and the philosophers stone had affected him more than he'd realized.
Well, good thing this is a dream, otherwise, he'd be well on his way to screwed, considering he was apparently in the middle of a bloody battle between wizards and ancient looking Vikings. Well, the Vikings themselves weren't all that old, just what they were wearing and fighting with looked like old pictures in the history books Harry had started checking out of the library, after he learned how terrible being taught by a ghost was for his potential future grades.
Hell, he didn't even have his wand, and was wearing nothing but one of Dudley's old shirts and a pair of ratty old pants that were big enough to look like bloomers.
That was okay though, this was just a dream, and since Harry knew it was just as dream, it meant he could do any spell he wanted just fine without one, right? Right. So, what spells did he know that could help here?
The answer was, not much. Quirrell had been a terrible teacher, and had only covered theory all year long. Harry had read ahead, and tried out a few things, trying to work his way through it. Some spells worked, but there was nothing that would do any good here. Oh, except maybe, what was that spell quirrelmort had used to tie him up with?
Oh!
INCARCERUS!
Thank Merlin, that worked. It also brought the attention of more fighters....
Harry, not daring to try and think of a new one, just fired the spell at anyone who tried going after him.
What felt like hours later, a pile of bound up Vikings, presumably, screaming obscenities at him in a language he didn't know, lay at his feet. Harry, despite already being asleep, had never been more tired in his bloody life. He was totally going to blame the exhaustion on why he forgot about the wizards.
"Our gratitude child, for your timely aide. Tell me, who might you be so we may thank thee properly?"
Startled from the man speaking behind him, Harry whirled around and managed to trip over his own feet like some newborn faun.
"Merlin! Don't sneak up on a bloke like that, nearly gave me a heart attack!"
"My apologies brave Merlin."
"What? No, I'm not.... You know what, never mind. Where is this?"
"This young Merlin is our land, where we have settled to build our fortress. How came you to be here, dressed so in strange rags."
"No idea, just sort of, uh, woke up here I guess..."
.....
The dream seemed to go on forever, even falling asleep in the dream did not wake him up in real life. Time also seemed to move like it normally would outside the dream. Harry finally decided that it was probably because he was so aware of the dream that things seemed so normal, well, not totally normal, because the place he ended up turned out to be the future site of Hogwarts, and the man who had spoken to him, turned out to be Godric Gryffindor.
Harry was content to stay though, and help the future founders of the first home he'd ever really had plan and eventually build that home.
In a funny little twist, Harry also taught the founders the two spells he'd used in the battle he woke up in. They in turn taught him some of their own spells, though they didn't have many wanded spells, since apparently wands were hard to come by, and even harder to make, only Helga had one, and she shared it between the other four founders as needed.
Godric, who specialized in battle magics, used his sword to channel his magic through. Rowena used a crown looking thing called a diadem. Salazar used ritual magic, something that seemed like a cross between potions and the base of future spells, just with a lot of components to keep track of, and requiring tons of time to cast.
Each founder taught Harry, masquerading as Merlin, a little bit of their types of magic. They were really good at it too, because in his time there, he learned more about each ancient and obscure type of magic than he'd learned his entire first year of his contemporary magic at Hogwarts.
"You guys are really great teachers."
"We must confess, we have greatly enjoyed our time teaching you young Merlin. Perhaps-"
Harry never discovered what that perhaps was though, as he finally woke from his dream, back in his bed in Gryffindor Tower.
_____
The second time it happened, Harry had been trying for ages to fall asleep. The ill fated dueling lesson the week before, when he spoke to a snake, and learned he wasn't speaking English, but some hissy snake language that apparently meant he was evil, because Salazar Slytherin and Voldemort both spoke it, and everyone knew they were evil! (And if Harry preferred his dream version of Salazar to the real one from history, who was to ever know. He'd take the goofy, slightly clumsy, patient but calculating man, over the bloke who wanted to get rid of all the muggleborns or at least not allow them in his school.)
Finally, in the wee hours of the morning, Harry felt himself finally nodding off. Only to jolt awake laying on the cold hard ground.
Harry groaned, and snapped his eyes open, to see a group of people surrounding one person tied to a wooden pole above a pile of sticks and hay, and, oh shit, okay, this. This was bad. Fuck his dreams for manifesting his fear of everyone hating him for somehow being like Slytherin, as his good friend Salazar tied to a stake, about to be set on fire.
All the rage Harry had been feeling at being ostracized the last week, the burning want to retaliate as he was being hexed and cursed in the halls, and sometimes even in his own common room. His need for someone, anyone, to for once in his life, stand up for him, protect him, help him, (want him) all came bubbling up to the surface, and for the first time in his life, he finally let go.
His magic ran wild, responding to his every thought, his every whim. In seconds his friend and mentor, strangely at least a decade older, was by his side, no longer tied and waiting for his death.
The people that had been surrounding him let out a cry, and several of them drew weapons, before rushing at him. Harry stood his ground, and with a wave of his hand thundered out "EXPELIARMUS!"
Suddenly, dozens of swords and daggers came speeding towards him, forcing him to duck down so they could sail over his head.
The men, though terrified, seemed undeterred though, and continued on towards him, some picking up flaming torches on the way.
Harry didn't even take the time to get back to his feet, he merely held his hand out again, and picturing the giant boa constrictor he'd accidentally released at the zoo on Dudley's eleventh birthday, he hissed out "~serpentsortia~". Four twenty foot long snakes popped into being before him, and Harry, hissed once more ~kill them~"
Seeing the snakes, several of the men ran, those that didn't were soon screaming and bleeding on the ground, the spots where they had been bitten turning black and rotting away before their very eyes.
Within minutes, the clearing was silent once more, save for the heavy breathing beside him of a panicking Salazar. The man's struggle managed to snap Harry out of the miasma of rage, and focus his attention on his friend.
The look the man was giving Harry was not one of fear though, as he'd expected, but of... Relief. Seeing Harry looking back at him, a whispered hiss of ~you are alive~ in the next moment, Harry was engulfed in the second, but best hug he'd ever had, in living memory at least.
Tentatively at first, he hugged the man back, his grip growing stronger with every passing moment though, until he was clinging tightly to his friend, sobbing into his chest.
After some time of sitting there, three of the four snakes came slithering back to them, and surrounded the two parselmouths, keeping watch for any dangers.
____
Harry returned to Hogwarts with Salazar and their three new serpent companions, who had asked to stay with "the speakers" and help protect them.
Hogwarts, though not as large as the one Harry had fallen asleep in, was far more finished looking than his last dream like this. There were also many more people inhabiting the castle. There were more dozens of people living there, or in the village nearby situated in an expanded clearing on the other side of Hog Woods, the forested area that surrounded Hogwarts on the sides.
All four founders were ecstatic to see Harry, or Merlin as they believed him to be, and after a few days of creating and catching up, Harry happily joined their school, teaching the two new spells he'd cast to help free Salazar, and learning as much as he could.
Salazar himself out him up in his personal family wing of the castle, introducing him to his family, who all adopted "Merlin" as one of their own.
Harry's dream felt as though it lasted for years this time. He was able to witness Salazar's three sons and twin daughters grow into young men and women, though he himself did not age, not even a day, because dreams are weird like that.
He'd been in the dream for what felt like a decade at least, when he was asked to attend a meeting with Salazar, Helga, Rowena and Godric, to settle on an official charter for the school. The four founders had been debating for years over what the charter should hold, each of a differing opinion on who they should allow into the school and what they should teach.
Merlin watched on as the for debated, and distant memories of what was currently happening in his real, awake life, he offered his own opinion.
"I understand the security risks of inviting mundane born wixen to study here. Perhaps though, if we were to have the students and their mundane families swear to an oath of secrecy, before allowing them a place at the school, it would help keep us safe, and allow them to be educated as the wixenborn are."
The four ruminated on idea, and finally agreed to add it to their charter.
When the last voice of agreement sounded, Harry awoke, back in his bed in Gryffindor Tower, Ron shaking him awake, late for breakfast.