Answer:
one for physical is that your muscles will seize up or cramp when you try to move. one for mental is that if your always sitting down you will most likely become stressed or get depression
Step-by-step explanation
the reason your muscles cramp is from lack of exercise form sitting they get used to that position and want to stay that way. then theres the deprestion ive had it it aint fun nor is stress ive had that too