Personal Space invasion on flights

I have a suggestion and a complaint, my flight from Dubai to Bangalore this weekend the person sitting next to me was so large they literally sat onto of me, i could not move and was so uncomfortable, i paid for my ticket as well and deserve a comfortable flight where i dont have someone pushing into the arm rest do hard it literally bruised my leg, i am a big human as well but i fit into my seat, IF somebody who is large and lovely and too large to fit into one chair THEN its only fair that they should occupy 2 seats instead of totally invaiding somebody else's space.. This is something that needs to be addressed, i have a looonnggg flight back tonJNB next week and am dreading the same issue