I'm feeling this a bit at the moment also. I started work again after not working for ages about a year ago. I tried to take things slow and took a job that wasn't too stressful and no too many hours a week. Ever since then I have been trying to push myself a bit to do more and for the most part I have been managing.
However, very recently things have taken off, I've taken on extra work, been covering other shift. Just this last week I have felt completely overwhelmed and worried things are getting on top of me. I just worry about everything and getting everything done on time and being perfect. It's really hard to shut off when I am not at work. The stress is causing my back to hurt even though I know it's just they stress and nothing wrong with my back it still hurts. I've been thinking of wats to get out of stuff like telling people I can't do stuff and taking holiday but I really don't want to let people down and also what I am doing it less than most hard working people so I feel I should really be able to do this.
Have you thought about doing something to make each shift comfortable for you? If you think a chair would work then maybe ask for one, I know it's scary, I hate to ask it makes me feel I am not up to the job. Can you take a little mascot in with you like a little plushie or something you like and sit it on your counter. It might give you some comfort and also spark a friendly conversation with customers. I would defintely talk to people about your situation, like co workers or a manager if you are struggling.
It's something you need to get under control though otherwise you will worry about each shift, That feeling of being trapped in a situation you hate will start to cause you a lot of anxiety so you need to turn it into a situaton where you at least feel comfortable, like it's work so it doesn't need to be enjoyable but you shouldn't feel dread at doing it each time.
