I didn't go to my doctor in the end. Over the course of today it's gradually faded away and it's now fine. Some of my coworkers suspect it's my new memory foam mattress that arrived yesterday. Apparently if you're not used to it you can get back pain :(
It's meant to be comfortable, and it really is, it's how I imagine sleeping on a puffy white cloud. Today I woke up with a back pain but it's far less severe than yesterday. Looks like I just have to get used to it.