Anxiety and panic really takes it out of you, it's exhausting. When I have a panic attack, whether its during the day or night and even if I manage to sleep for a good few hours after, I always feel as if I've not slept at all.
Being constantly tensed up all the time isn't going to help, it's like doing a strenuous workout every day with no break.
I'm not sure how to explain it to your mum, you have to explain how it makes you feel as best you can and say that it's not you being lazy and that while her ways of dealing with things might work for her, it doesn't mean they'll work for you. Everyone deals with it differently. Some say going for a walk or a run or punching a punch bag helps with panic attacks but I can't do that during mine. I can't move when I have one. The only movements I make is uncontrollable shaking. It's not as easy as it sounds, physically doing something when you're that anxious or panicked.