That might not be it at all, but here is a possibility...
I had most of the symptoms you describe when i became severely deficient in sodium and salt due to stopping ALL consumption of it, and doing a lot of physical exercise... it threw off my sodium/potassium ratio so much that i got light headed, brain fog, no digestion, and felt very bad overall...
So, just in case you are avoiding salt for some reason, you can give a try to good Sea Salt and see if your digestion isn't improved...