I get this quite frequently too, mainly when pregnant. I don't know what causes it but the only thing that works for certain is taking a paracetamol tablet. Just one, even though the recommended dose for adults is usually 2. (Apparently paracetamol is safe but i don't like taking medicine if I can avoid it even when i'm not pregnant). This reliably (for me) takes about 20 minutes to work and it doesn't come back for the rest of the night. It's a truely wretched condition and i even sometimes get it in my shoulders! meaning i can't lie on my side (or still at all). Hope this works for you!