I’ve had this problem off and on for years. The fact that it’s not constant gives me hope though. I try the meds the doctors prescribe. Some help, but not all that much. Some, I’ve had such a bad reaction to that I just can’t take them. What’s surprising to me is that on good days, I can move about normally. But, on bad ones, even walking a few feet is so exhausting that I have to sit down.