I got to see a bone marrow biopsy today. And I totally blacked-out about 2/3 through it. I saw the needle go in. I saw them take 2 samples. Then I realized that my breathing was getting a bit shallow. No dizziness. No tingling on the neck. No wooziness. So I backed up to a wall and was in the process of sliding down to a squat when I completely black out. And coming to is really disorienting. For a few seconds, I couldn't remember where I was, or what time it was, or if it was all just a dream.
Later, my supervisor/boss said: I think you are emotionally drained, I'm really worried about you. It felt like it came out of no where.