I Experience E Occasional 'spells' When It Feels Like A

I experience e occasional 'spells' when it feels like a heavy weight pressing down on my shoulders and upper torso. I get a little breathless and feel like I have no strength to lift my arms. This has been probably 20 times in the last 12-18 months. There is no acute pain and the event lasts only two to five minutes. Afterwards, I feel completely normal. I wore a 30 day heart monitor, but had no occurrences during that time. Even had a heart catheterization. Any suggestions?