OP, I really understand what you are saying and relate to it. I consider myself a bit 'aimless' too, I was clever and found exams easy so I went to university because it was expected, did a PGCE because I had to do something and now I'm in the same job you mention. Not a vocation, but I've always been good at it and been successful, though ultimately I have always viewed work as the means to an end.
People saying that work is a source of self esteem aren't considering the flipside, which is how work can utterly destroy your self esteem and sense of who you are. High stress, unmanageable workload, exhaustion. I used to regard my job as benign, now I've returned from maternity leave with what was a relatively mild case of PND which has now spiralled into a much darker, more severe depression. It's the grind, the pressure, the relentlessly exhausting juggling of responsibilities. I'm up now, have been up since 4am consumed with anxiety. The night before, I was up all night. Work can ruin your life, it isn't the cure-all that some people are suggesting.
Which isn't to say that I agree you should just decide to never get a job again. But you've experienced a severe illness, take time to recover without stressing about what may happen in the next few decades. Think about the kind of things you'd like to do, without turning it into the pressure of choosing a career. People have raised important reasons to work - independence and security later in life for example. If I were in your position, I'd take time to focus on my recovery and take it one step at a time. You may well come to paid work again but there is no need to agonise about it just now.
Depression can definitely be exacerbated by not working, I'm sure, but ime work can make it considerably worse as well. If you're not someone with a particular drive and attachment to a job in the first place, then it's not the place to seek out validation and self-worth. Maybe you will find a job that provides that, at some point. But right now, why not find the things that you enjoy and want to do, without pressure? By not working now, you aren't deciding to never work again.