[Yarmark]

1. Sounds related to chi. Burning / cold in the main channel has been related as symptoms to me by a friend going through advanced chi kung / qi gong. I don't know much about this topic, sorry... he mentioned that intense icy cold is what happens when toxic energy is not draining through the proper channels. Fire seems related to a raising of energy. I broadly generalize.
2. This has been mentioned as a physical side effect of bringing lots of energy through the base chakra. Irritating perhaps, but harmless... if but a good warning to slow it down. I once had an energy rash burst open along an acupuncture median all the way from my wrist to my heart. It was not painful or harmful, but it left scars for quite a while.
3. I see this as well, usually as a purple/greenish spot. In advanced states of relaxation/meditation, this spot for me will become like a pane of window glass, offering views to scenes. I have also seen the "film negative" effect you have mentioned... this is a precursor to states of clairvoyance. The picture starts as black, with motions like pixels of color against the black, then it becomes sort of gray/b&W, then it resolves into full color.