Hi, I can see a couple problems going on here. The first is easy to solve. You're setting yourself up for disturbed sleep by falling asleep the way you do on a chair or sofa. I take it this means before your bedtime. But whether it's before or not, what happens is you wake up in an hour or so and your brain doesn't know what's going on. Maybe you've already entered a dream phase. Whatever the case, your brain gets confused. I'm sure this isn't all of the problem but it surely makes it worse.
You need to stay awake and alert until your normal bedtime. It will help if it's not too early so you're really tired when you do go to bed. Then go to sleep in your bed, in the dark and your chances of staying asleep will be greater. You may still wake up with a panic attack but I bet your period of sleep will get longer and longer.
The other issue is breathing. You should learn slow breathing and do it for 15 minutes before bedtime. Then do it immediately again when you wake up disturbed. There's nothing that will relieve you more than this. It's the ultimate coping mechanism.
But this has to be learned the right way. I recommend the Breatheasy system. It combines slow breathing with music. Nothing else like it. You can get free instructions plus an online audio demo at
http://www.control-your-blood-pressure.com
/demo.html