Lacking the possibility of damage, the first thing to suspect is a swelling battery. That is an emergency situation because bad batteries swell at a very rapid rate and with enough force to render the computer irreparable. They require an immediate evaluation by Apple.
This is my checklist of things that can indicate a swollen battery:
•Unexpected trackpad and/or keyboard behavior.
•The gap between the display and the deck is not even when the display is closed.
•The gap between the bottom plate and chassis is uneven in places.
•Some of the screws that hold the bottom plate have popped out.
•The trackpad surface is higher than the surrounding deck surface.
•The computer "rocks" a bit when placed on a known flat surface.
I find solid-surface and granite countertops very effective flat test surfaces.