I agree with angie, it may have been over-excitement, but still, congratulations on your first lucid dream!!
And like she said, calming things can really help you stay in the lucid dream longer if you are getting over-excited. Like absorbing your surroundings and touching things. Even better is to look at your hands while you do these stabilization techniques. Looking at parts of your body while you're lucid really helps you lock in your form, sustaining the dream. Especially if it starts out kinda fuzzy.
Good luck, and happy dreaming
~ophelia
Bookmarks