Why is my iPhone screen popping from the opposite side of the battery?

So I noticed today a slight pop on my screen, a slight curve upwards when I saw that the top right side didn't fit my case.
My IPhone5s has the power button on top of the curve I'm Talking about and the sound buttons on its left. That's where the battery is supposed to be too so I don't think it's caused by a swollen battery, any clue on what it could be and if it's dangerous?

Its getting old, you need an upgrade

If it's not caused by a swollen battery you should be able to just snap it back into place. If it won't go it's because it has a swollen battery

I would call your phone company and ask them about it

Contrary to what you think that is EXACTLY what a swollen iPhone battery does.

Swollen batteries are dangerous as they become a fire/explosion risk so you need to replace the battery. Explosions are usually just a loud POP! Sometimes followed by a very hot fire which should not be doused in water but instead extinguished covering in sand from
a fire bucket or by using a dry powder extinguisher.

Until then, NEVER leave it charging whilst unattended, NEVER charge it on a flammable surface, and don't do silly stuff which you should never do anyway like sleeping with the phone under your pillow.

It may make more sense on a 5s to just replace the entire phone; also due to the risk of the battery destroying the phone make certain you have it fully backed up to protect your data.