Hey Bud,
Welcome to the DhO.
Going by your descriptions, I'm assuming that you have some knowledge of the standard maps of insight practice commonly discussed on here; I'll suggest that you have just crossed the 4th ñana, Knowledge of the Arising & Passing Away, as your descriptions sound typical of this stage. If this is the case then it indicates that you are practicing well enough to be making progress and so, assuming that you haven't yet attained stream entry, you're on the right track towards enlightenment.
If you haven't already done so, I highly recommend checking out Daniel Ingram, the founder of this site, and his book
"Mastering the Core Teachings of the Buddha" which is an excellent starting point for anyone looking to learn about pragmatic/hardcore dharma and get results in their practice. In particular, I would suggest reading
this chapter and seeing if any of it sounds familiar to you.
Either way, don't panic or think that you're dying or anything silly like that, this is just a natural part of the process but the stage you've just experienced is a turning point for anyone interested in 'getting' enlightened so it, and the potentially difficult, but not inevitably so, stages which follow it.
Why not start a practice thread to keep track of how you're getting on, it's a good way of learning and you can get some excellent advice from people who've walked this way before.