my husband is 65 years old, 6ft2 240 lbs. is a veteran and is on medications for PTSD, chloresterol, thryoid, blood pressure. His b/p is usually good but lately has been experiencing low blood pressure readings for hours at a time. example 83/59, 78/60, 90/66, 78/61. He claims to feel light headed also. His prescription for lisinopril is 10mg. What could be causing this drop in b/p for hours at a time?