That pain was just a hallucination. Its nothing to be afraid of worry about. The best thing to do is to completely ignore any type of unpleasant hallucination. Try to think about that table again or anything to get your mind off the hallucination. Repeat to yourself, "This isn't real, it is only a hallucination." As for the sawing off your arm, that is very unlikely. The mosquito pain was able to manifest because it is something that has fairly high odds of happening. You thought, "maybe there really is a mosquito on my face." This caused the hallucination to become extremely real. I am pretty sure you are not going to think, "Maybe there really is a man sawing off my arm for no reason while I am sleeping." You did an excellent job to be a beginner. Just try to think pleasant thoughts as you continue to drift toward sleep. If you have any further questions, don't hesitate to ask!