I've had/am currently having that same problem. I don't think its any apps that I've installed recently as its not always happening, and that has been the problem before. I think its happened a couple of times with apps not being killed, especially the HERE maps and drive apps. I've power cycled it a few times and that's seemed to have helped. Do you also charge it up to 100% all the time? I've noticed my phone will heat up sometimes if I do, and I'm running the official Cyan update. Let me know if any of those work for you!