Been a few hours now and I have gone out and checked it every hour and all is still well. No lights, responds to my key etc. I'll keep watching it closely and come early next week I'll have the battery tested and replaced. I have had the car about 2.5 years now, and the battery was probably at least 2 years old when I bought it, so it's a good chance it's on its last leg.
I'll have it tested anyway just to see what comes up (going to replace it no matter what) and report back with my findings. Hopefully help others in the future.