Why am I dreaming I have an exam I didn't study for?

This time next year, Oluwatosin, 17, will be taking his A-levels at Leeds Sixth Form College.

And he knows that as that time approaches, he will have the same recurring nightmare.

Oluwatosin finds himself in an exam hall, his maths paper in front of him, but he has confused his revision for statistics and mechanics and the test is full of questions for which he has not prepared.

He wakes up, sweating and with a headache, relieved to find that it was, indeed, all a dream.

There is no way, really, of knowing just how common dreams about exams are because not everyone remembers them.

But why do we get them, and is there anything we can do to stop them?

Colin Espie, professor of sleep medicine at University of Oxford, says our brains are awake even while we are asleep. They are busy cementing things we have learned, building on our memories and processing our emotions.

But they also produce "output", or what we know as dreams.

"We tend to get little insights into the fact that our brain is working on material," he says.

Dreams about exams should help "reassure" us , therefore, that all that learning is being done - even without us knowing it.

"What's happening during the night is, maybe your brain telling you... 'I know it's concerning you, I know there is content to be done. I'm working on it'," he says.

"That's not to say that we shouldn't be studying during the day. The brain can only consolidate things that we're trying to learn."

We may have lots going on in our lives, so why is it that exams can stand out in our dreams?

"It's a common theme to dream about anything that is threatening," says Prof Espie. Just because something is threatening it doesn't mean it's bad, he says, but it can mean it's challenging - and exams are, almost by definition, challenging.

"For most people, they don't look forward to their exams, right?"

"It's on your mind during the day, and it shouldn't surprise us that it's on our mind during the night."

Exam dreams are quite common, according to Prof Espie. "Pretty much" everyone has dreams even if they do not remember them.

"For a proportion of people those [exam dreams] are not breaking into consciousness, so you're not aware of them at all," he says.

"For some people it will be breaking through a little bit more and it will be occasional, and for some people it will be an every night problem."

Zuhal, 19, often dreams that she is running late.

"I wake up two or three times before my alarm to check the time," she says. "I think... I need to sleep for another hour, but I can't."

For Prof Espie, the explanation is "quite simple".

"You can tell the time, even when you're asleep," he says - adding that human beings haven't had smartphones or even watches and clocks for very long in the scheme of things.

Nightmares, he says, are emotional dreams - a sign that our feelings are being processed while we sleep.

Some can linger for years, including those about exams.

They can sometimes be "triggered" by similar emotions and "senses of being stuck", says Prof Espie - although they can occur randomly.

"Our brains categorise things," he says.

"When people come across other difficult situations, they'll reflect back and think, 'yeah, I had a similar thing when I was at school and I did exams'.

"An exam dream later might not be to do with... an examination, but might be all to do with being tested in some way."

So what can we do to try to stop nasty exam dreams?

Well, if you do actually have exams coming up, Prof Espie recommends having a good study timetable with regular breaks so you can "reassure yourself" that "you have a plan, and you're putting that plan into action".

And avoid cramming late at night

"If you tumble into bed with formulae for maths going round and round your head, there's a good chance that you're waking up with them still on your mind in the middle of the night," Prof Espie says.

"Give yourself a wind-down period."

You can also try being "compassionate" to yourself when you wake up from a bad dream.

"Anxiety, generally speaking - whether it's our anxiety during the night or it's anxiety during the day - tends to take the same form, which is, 'what if?'," says Prof Espie, who also specialises in the relationship between dreams and mental health.

That might be why you can dream about situations like running late for an exam or not knowing any of the answers.

"We need to think about our response to that," he says.

"If we're asking that question to ourselves, we'd probably just think, 'well, you're stuffed then, aren't you?'. But you would never say that to somebody else."

Rose, 19, does not get exam dreams - or does not remember them - but exams still disrupt her sleep. She often finds herself still awake at 2am.

The only fix she has found so far is watching Rick and Morty, one of her favourite TV shows.

"It just calms me [and helps me] to go to sleep easier," she says.

Prof Espie says it is impossible to make yourself sleep - you can only ever fall sleep.

If you do find yourself staring at the ceiling at 4am, he recommends flipping the way you look at it. Try to be relieved that you get to sleep for another three hours rather than worrying that you now will not get enough sleep before an exam.

If you can't, take about 10 minutes (without using a phone or watch to time it) to allow yourself to fall back to sleep.

And if you still don't?

"Get up for a short period of time, until you feel sleepy again. Go back to bed, and allow yourself to fall back to sleep, reassuring yourself that it's OK to have woken up," Prof Espie says.

"Just don't get caught up in a vicious cycle of trying too hard."

He says that if it is the middle of the night, you are likely to still need your sleep and it will come.

"Don't overreact to events that happen during the night," he says.

"Trust your sleep."