It takes time to get used to. Here is what I recommend:
- Inhale as you reach for the floor.
- Find your balance.
- Exhale and try to breathe deeply.
- If you lose your balance, focus on balancing and breathe again once you're stable.
Breathing will be easiest once you are nicely balanced.
If you need to walk around, you're breath will be irregular, but it shouldn't be too difficult.
If you are struggling to stay up, it will be VERY difficult to breathe.
Generally speaking, people tend to hold their breath while concentrating on something. It is done unconsciously and causes physical and mental strain which ultimately disturbs the concentration.