Panic after resigning from a toxic workplace

I'm typing this out as a way of collecting my thoughts and feeling a bit normal to take myself through the day. Context: I have been working with a small b2b IT firm for the last 1.5 years, and resigned yesterday. This was my first job straight out of MBA and it has sucked the soul out of me to say the least. The notice period is 3 months and I am really unsure how will I survive it considering that I'm already completely drained.

I do not want to list out the reasons of how this place has been toxic for me because I also carry a lot of self doubt if it was really the toxicity of the place or my own incapability to handle the work. I do not have any offer in hand, and haven't started a job search either. Just wanted to put this out there to see if people here in the community have been in a similar situation in their professional lives and how did they figure out the uncertainty, was it a good decision for them in retrospect and if they have any tips for me to deal with this better, with less anxiety.