Yeh, this happened to me a few times, not from the pain but the very low b.p. when I’d get up in the morning with uber cramps. Sometimes they would be really, really severe. Other times ‘normal’.
I take ibrupofen tablets. Eat well and avoid cold things, if I couldn’t be at home with a hot water bottle I found Cura Heat patches indispensable. I’d use the back pain ones as they were a lot bigger than the period pain ones.
And I find the activity thing is nonsense. Cramps are going to get ‘lesser and lesser’ over the day regardless of whether you are active or stay in bed.
When I was at school, I would get severe muscular cramps in my lower back and thighs, I couldn’t even walk up or down the stairs without one of my friends helping let alone go for a walk or jog.