Congratulations. Hope your first 3 days in the new job have been enjoyable.
I can relate to your situation somewhat, although from an outsiders point of view. My wife suffers from depression, a few months into 2016 her job role changed (office changing their procedures) and she ended up having to take a more managerial role, something she was very unsure about. Sure enough a few months into that role she was struggling with the managerial side of the role - this lead to an onset of depression, culminating in me having to drive home from work, when I got a call from her office saying she hadn't turned up for work, or got in contact - and she wasn't answering the phone.......That was a horrible journey home for me (over an hour drive...). Thankfully she was in bed, but in a real, real deep depression.......she ended being signed off work for 6 weeks and had to up her dosage of anti depressants. She went back to work, but the damage was done, another 2 weeks later and she was back at home, this was probably a year ago. She spent Christmas off work.
Long story short - she ended up leaving that job and surprisingly getting a decent settlement. A few months off work without the pressure of knowing she'd have to go back to that job did the would of good. Around May this year she managed to get herself another job in a much smaller office, and it's worked out real good so far, she's much happier and the depression has stayed at bay.
My wife once described her experience of deep depression as being at the bottom of a well, looking up you can see a pin prick of light, but instead of wanting to climb up, she just wants the light sealed off. So yeah any environment that spirals your mindset towards that is important to get out off.
So Congrats again mate, and all the best in your new career.