Also:
You do not have to ace the interview just show promise.
What I mean is, even I've gone through interviews where I didn't know all the answers and they still kept wanting to follow up with me. Don't be too harsh on yourself.
Absolutely this. The primary purpose of the interview is to establish whether or not you are competent enough to do the job. This doesn't necessarily mean having all of the skills out of the box, but whether you are capable of picking them up and have the basis to do so. Best piece of advice I could give is don't lie. If you don't know the answer, say so. But, better to follow up with "...but, this how I think it might work" or "...but, this is how I would go about finding the solution".
One of my purposes in interviews was literally to get the candidate to say they didn't know. We can work with people that know their limits; can't work with a bumbling fool that knows no bounds.
This. It's ok to admit you don't know everything in an interview. Some of my most glowing feedback from interviews came from interviews where I answered questions with a flat out "I don't know"
I ended up taking about 2 years to examine and reflect upon my situation. Meditation played a huge part during this time. I traveled, explored new hobbies and ideas, and experienced different ways of life. I eventually ended up moving back home to live with my parents as I continued to sort things out.
Currently, I feel much more stable and have a clearer idea of how I want to move forward. I now have a plan to move out and pursue a career utilizing my degree and feel very excited about the future. Taking time off to reflect in this way has been indispensable for me.
By all means see a counsellor or a psychologist, but unless you have deep psychological issues where you are getting to an unbelievably unbearable point where medication might help you, see a psychologist first and leave the psychiatrist out of it.
And, in case anyone thinks I hate psychiatrists - I don’t. I just feel they aren’t that helpful in the sort of situations you describe here.
Unfortunately, for every great psychiatrist, there are just as many truly awful ones and despite their medical degree they can totally botch your diagnosis.
That’s my opinion anyway, take it as you will.
For what it's worth, antidepressants have a very valid part to play in the treatment of depression, as do various other psychopharmacologies. I've taken medication for performance anxiety in the past and it helped me overcome some real challenges.
That said, talk therapy with a good psychologist is also very useful both alone and in combination with drugs.
A lot of the other posters have given some great advice from a technical perspective. I'd suggest taking some time to evaluate and improve your mental health as well. If you're putting yourself under so much pressure, that pressure alone will hold you back to a great extent.
First off, just relax. Take a little time off to reset your psyche, overcome your burnout, and rediscover your confidence/interest. It's amazing what taking a week off can do.
Take up some activities that have been shown to help with stress relief. Meditation. Exercise. Long walks. Digital disconnects. Healthy sleep cycle.
Read this book: The Inner Game of Tennis. It's a short read, but it will transform the way you approach high-pressure situations.
You mentioned PTSD - do you actually have PTSD, anxiety, or other similar mental health problems? If so, talk to a counselor or find some way to address those underlying issues.
You have a long career window ahead of you, so don't burn yourself out at this point. Job prospects are great for CS majors, and you seem like a guy who's very motivated and hard working. Spend a bit of time taking care of yourself, and I'm sure you'll be fine in the long haul.