Memory Issues 

You wake up in another place.

And a completely different body.

Your significant other or significant other the person whose body you are inhabitating now, is doting, caring, and attentive, and assures you the amnesia is not a problem for them.

The doctors told them it might wear off soon! And everything will be ok again!

Something feels slightly off but that is just the new body and strange circumstances, right?

Can be that the original owner of the body was kidnapped and is now in the hands of their worst enemy.

Like the nemesis of a superhero trying to turn them to their side now that they have the opportunity.

Or the original got kidnapped by a stalker.

Can be an obviously socially awkward staller.

Or someone very dangerous, think of the yandere archetype.

Or a sociopath who has adapted enough to appear charming by going through the motions but can't always hide the slipups in such close quarters.

Or they got into an accident and their emergency contact was still set to their ex.

Should make for a lot of awkward moments and leftover feelings spilling over from the ex.

Whatever those feelings are.

Or, in a completely different plot twist, the amnesia is the real thing and what is making everything feel off.

The significant other is really just a caring partner and no dimension travel or similar took place. 

It could all be interesting, turning more into psychological horror or very wholesome, depen

ding on which way it goes.