Sounds to me like you are a completely normal person, having a completely normal emotional response.

Of course it is good to make sure that it is not one of the medications you are taking or something else that could be going on, but you have just had a fairly traumatic experience and out of the relatively protective environment of the hospital, finding yourself at home, wanting to go back to your previous life and activities and finding yourself more ill than you planned.

Just give yourself time, don't push yourself to do what you feel you can't.
when you wake up terrified, just remind yourself that this is a nightmare, just like you would if it was your grandson coming and telling you about the monster hiding in his closet.

What a sweet and sensitive grandson you have, bringing your favorite toys.
I am sure that this warms your heart and reminds you of why you want to make the effort, go through all this and get better...

Also, make sure that your breathing is OK, because possibly you are waking up in the middle of the night because of true breathing difficulties and not just being afraid of having them. This could also explain why you feel apprehensive when making a more significant physical effort (such as going out for coffee, which for you now is probably similar to climbing the Everest) So, maybe if there is no improvement a proper respiratory evaluation and a sleep study would be in place.