I've Noticed When My Stress Levels Are Really High For

I've noticed when my stress levels are really high for long lengths of time, I experience these odd episodes. They last only a split second and have happened while I'm doing a variety of activities both sitting and standing. It usually happens that suddenly I'll have this dropping feeling like I'm a marionette who's strings were just cut, my head feels light, my heart kind of clenches (although I don't know if that's from the falling sensation, the episode, or both), and my vision blacks out. Like I said before this all happens in the span of a click of your fingers and I'm right back again as if nothing happened, but it's very concerning. It sounds like a fainting spell but can you really faint and recover that quickly?