my laptop was running well and everything is fine and games working well (dell inspiron 5567 i7 processor)

but suddenly somehow my cpus starts hitting 100% usage while playing same games that was working well before!...it hits for few minutes then go down then go up again..i dont understand whats going on really..when i open task manager i see only the game working or taking most of the cpu usage but that shouldnt be happening everything was okay...so please i'll be happy to listen for solutions