This is something I can relate to completely. I was terrified of returning to work, and am still working towards gathering the courage to return to paid employment out with the general public.
In my experience, volunteering is hugely useful. I was lucky enough to be able to do voluntary work with people I know, and that made it immeasurably easier for me. It might be useful for you to ask amongst your friends and family to see if anyone you know needs volunteers at their workplace? Having the support of someone you know and are comfortable with during this time is a huge help, and the feeling of taking control of your life and doing something beneficial for others is a massive boost, especially if, like me, you are also suffering with depression (it seems to go hand in hand with anxiety more often than not).
If you are worried that returning to work full-time seems like too huge step, working part-time may help you ease back into work - I currently volunteer only a few hours three days a month, and it has helped me to regain some of my confidence dealing with people I don't know, and has also resulted in new friendships, which I was badly in need of after cutting almost everybody I knew out of my life as my illness worsened.
There are also many employers who are mindful and sympathetic to the problems faced by people with mental health issues, and who can and do provide support in re-employing and keeping people who have been away from work, or have a high turnover of jobs in the past by reason of illness.
There is every reason to stay positive and to do your best to "get back on the horse" - in small, gradually increasing steps if necessary - there's no need to take on something you find overwhelming all at once if you can break it down into smaller, more easily achieved goals. Each of those goals you achieve will make you feel better, and make the next step seem less and less difficult. Many people (myself included) worry that going back to work may be too stressful, that we might somehow relapse and lose the progress we have made in dealing with our illness, but a recent NHS study in the UK shows that the opposite is true - that returning to work offers huge benefits to your general health and wellbeing, and is a goal well worth working towards.
I hope I've helped in some small way, and I wish you all the very best in your journey back into work.