Suggest Treatment For Persistent Hypotension

Question : My 67 husband has syncope episodes in medically stressful situations where he falls, is helped up to a sitting position, and then looses consciousness and stares blankly... then comes out of it in about a minute (usually admitted to hospital for short time after for fluids). 1st time was 1 week after heart surgery (quintuple bypass 2011), 2nd time 1 week after bariatric surgery (2012) , 3rd time 1 week after dental surgery(2015), 4th time 2 days after 2nd chemo, 5th time 1 day after 3rd chemo, 6th time 1 day after 4th chemo, and 7-9th time in nursing facility while attempting to walk. We always thought it was low blood pressure, and it is definitely caused by dehydration (he's not eating very well due to the esophagus radiation and typically didn't after each of the above surgeries either)... but now he is in a rehab center due to side effects from cancer radiation & chemo treatment and it has happened 3 times in 3 weeks (time 7-9 above). They said that when this happened at the center, his blood pressure was Not low. They gave him IV fluids twice in 3 weeks also. For many years, he has also gone through times where he blinks constantly... may be unrelated though. Right now they can't rehab him to walk because his blood pressure is always low and they won't walk him if it is. He is on 2 medications to bring it up, but they are not working to do that very much. Do you think these could be seizures, and do you think they could be related to his heart or his brain? or does this sound more like dehydration? and do you have any suggestions for raising the blood pressures. About 3 weeks ago when in the hospital (prior to him going to rehab), they also gave him 2 units of blood because of low platelets after chemo then discontinued the last 2 chemo treatments... but he Did finish 6 weeks of radiation. He just had more blood work and depending on the results, I have asked them to consider more blood since that seemed to help temporarily. He will see his cardiologist this week... I am looking for questions to ask or important things to consider, discuss, think about or observe.