All decisions have some sort of risk. If you feel as though you are doubting the decision for your degree, it's perfectly normal.

It's also understandable if you're having issues with trusting yourself to make the right decisions, feeling uncertain after a decision is made can be uncomfortable.

If you feel detached from these decisions, that may explain part of the delusional feeling. Impulsive decisions can lead to feeling like your identity is not in alignment with certain aspects of your life, especially if you've made a few life decisions in a short amount of time.

You have mentioned at the end of your post that you have some mental health illnesses. Could mania explain any of these behaviors that you are describing?

I want to add that I am not a mental health expert, however I have had my own experiences of mental health challenges.