Feeling inadequate as a PhD student
Many universities have a &quot;counseling&quot; office that can help with such things. But, I agree that it is probably imposter syndrome as you have moved to a situation in which your peers are more skilled than in the past. You probably stood out from the crowd in the past and now you don't, most likely.
But you have affirmation, just by being where you are, that you are worth it.
It is hard during a pandemic, but developing some social relationships with your peers can help. When I was a doctoral student, some of us played paddleball, rode bikes, played softball, etc. just to help keep our sanity.
But if the pressures are mostly internal, you can also set limits that seem artificial. For example, exercise for an hour before lunch every day. Get some aerobic exercise for a few hours every week end - on schedule.
You may find that these breaks aren't unproductive to your work, actually. Your brain will continue processing &quot;stuff&quot; even when you aren't staring at a computer screen. In fact, too-long hours can be counterproductive, producing blocks.
Give yourself a break, but also try to talk to a professional.