I find that the hardest thing to determine - the outbreath falls away naturally, but I can sit there until it feels like I'm never going to inhale again, and at

I find that the hardest thing to determine - the outbreath falls away naturally, but I can sit there until it feels like I'm never going to inhale again, and at no point does it feel like my breath "returns" by itself, but rather I feel like I have to drag it in, while my heartrate spikes. I have been mildly asthmatic all my life, so maybe that has something to do with it. Incidentally I have often noticed my thoughts become agitated and realised that I'm holding my lungs empty.