So I know this question has probably been asked a bajillion times. But, every time I masterbate which is on a semi regular basis now, I work up towards the feeling of getting there and my legs start to cramp up and sometimes my back starts to arch and I make involuntary noises but then I feel like I end up stopping myself before “finishing”

I know everyone is like oh you’ll know but like is the body cramping it or am I just not able to quite get there on my own? Insight is greatly appreciated.