Self care vs laziness?

Hoping for some insights about how to know when I'm using 'self care' or a 'mental health day' as an excuse just to be lazy. I suffer with severe depression and work as a nurse. Due to covid my hours dropped significantly so now I only work 1-2 days per week. As a result if I have a day where I'm supposed to work and just can't face it, I feel incredibly guilty for thinking about taking the day off. I'm having a lot of trouble with my energy levels all round, my doctor has put me on melatonin to even out my sleep, which has reset my body clock but I still wake up feeling like I've been hit by a truck, even after sleeping 9 hours through the night. I don't understand why I'm so tired all the time. When is it healthy to force myself to go to work (or socialise etc) and when is it healthy to listen to my brain? And is it my actual brain or depression brain? How do I know the difference? I am trying to get better at listening to myself because making sure that I hear me takes away my external reliance and resentment on others not hearing me. But I am afraid of being judged for not working and I judge myself very severely. I even lie about my life and work hours so that other people won't judge or berate me. I'm also not very good at pushing through in order to build stamina and resilience, if I don't feel like something I generally don't do it. I'm such a bad person.