I was talking to my trainer about this on Monday. He said, if you hold your breath, the worst that will happen is that you'll pass out. And since you're doing push-ups you're already close to the floor so you probably won't hurt yourself. Although you might want to have a mat under you just in case.

(Yeah, he can be quite the wise-*** at times. And yet I've been putting up with him for over 11 years now. Of course if you asked him, he'd say he's been putting up with me.)

Anyway it sounds like you're doing a good job figuring it out. Keep practicing and before you know it, you won't even have to think about it anymore.