One of my docs back in my grad school days told me that some people with low blood pressure also have weakness/wooziness/faintness issues. I was having spells where I couldn't get out of bed for days when I went to him.
His suggestion was to make sure I was getting enough salt, particularly when the weather was warm or when drinking more water just made me feel more bloated and lethargic. I got some BBQ potato chips on the way home from that appointment, and I immediately felt better!
So if you have those symptoms, try eating something both safe and salty and see if you feel better. Gatorade (perhaps diluted 50/50 with water or seltzer), pickles, and baked potato chips are my favorite.