I discovered I could get my blood pressure back up to normal levels by eating salt. Usually a handful of salted nuts and lots of water gets rid of the weakness and dizzyness.

You can get pills f r on doctor for it my husband has them

double ditto on the drink plenty of fluids - maybe some with electrolytes if you're sweating. There are meds out there that raise BP reference to check out https://www.ncbi.nlm.nih.gov/pmc/articles/PMC36...

Have had that all my life. If you feel it coming on, sit down, or put your head down, hands on thighs, if you can't sit. Also, clenching muscles helps. I have to pause when I sit up, and when I stand, to be sure that my blood pressure has stabilized, before I move. I find that being well-hydrated makes a big difference, especially in hot weather.