Well... a long time ago, I didn't have much sleep and I was going to the beach with my dad. I had a wet-suit on and fell asleep. I had an EXTREMELY vivid lucid dream with FULL control. About a year later, I went to the beach again and got a lot sunburn and sun-poisoning. I had an extremely vivid dream but I didn't have much control. Anyways, heat or vitamin D may be a possible lucid aid, I'm not saying you should go out and get sunburn though. I'm just noting a possible discovery.