I believe that part of your approach when trying to Lucid dream is off. The key to your method is relaxation, and the best thing for you to do when trying is to just relax completly. Its sounds like youre getting the hang of it considering you got really far, but you need to relax more. Most of the time youre heart should be beating really slow unless youre attempting astral projection. But unless youre doing that try to keep your heart rate as low as possible- its a big part of getting in to the dream world. Also, when you start getting those signs and you start progressing in your attempt, just relax- dont get excited or anything. Dont respond to it, just let it happen. I know youre thinking, "Thats impossible" but its not, trust me i once thought that and with a little practice and effort it becomes possible. Plus supressing strong emotions of excitement and such are necessary in order to stay in a lucid dream, but dont worry its really easy, you just need to put in the effort. This may seems like alot but the only two points im trying to get across are- pure relaxation, and supressing your emotions during attempts. Hope this made sense. Peace