Cramping - when should I worry?

Helen
I'm 16 weeks 3 days and last night after waking up from a nap had a really painful cramp in my abdomen area which felt almost like what I'd imagine a contraction would feel like (first baby so I have no basis for comparison!)
It stopped after about 30 seconds but felt a bit tender. I'm aware of Braxton Hicks but it feels a bit early for that? Should I be concerned or can this sometimes happen? I don't want to ask Dr Google and get into a panic!
If it happens again I plan to call my Midwife but wanted to see if anyone else has had the same thing? No bleeding or anything and haven't had any pain since.