If you're compressing cartoids you are not gasping for air. I'd say it's a defence mechanism. You've done your research, you know what to expect, and when those first tingles wash over you, it could be too much to accept. Knowing you've found the 'sweet spot', knowing consciousness and ultimately death follow, but not following through with it.
When I'd correctly found my cartoids it was a mix of euphoria, knowing I could do it, holy f#ck what the hell am I doing etc. Just a thought.