What Causes Dizziness And Imbalance While Doing Activity?

i am not sure if it's motion sickness or not but i wanna make sure. i get it a lot usually if i lay around a couple days and do nothing. if i am constantly active such as doing football during the week and play a game i dont get it but after the weekend i get sick at mondays practice. i dont get a headache but i get just really dizzy and i feel off balance but if i rest and practice again it doesnt happen the rest of the day. it happens in games a lot and it really messes up my performance and i dont know how to stop it.