Ketamine is very different to mushrooms.
I've taken a fair bit of both. I know a lot of people who took too much ketamine, recreationally. I can't stand the stuff now. Nasty, synthetic, antisocial party smack.
Mushrooms - although I don't take them these days, I look back on them very fondly. Natural, lovely things.
Mushrooms are a much deeper experience - more spiritual, if you like. Taking a trip can genuinely give you profound insights into your life and the world. They are an experience, a journey you go on with those around you. Alternatively they can just be a giggle and a fun experience with friends. (Or a bad experience if you're unlucky / in bad circumstances).
Ketamine, o the other hand, is like a confused dream! And it all goes on inside your own head, it's not something you can really share with others. If you take a little bit you'll still be able to communicate with others, but if you take loads - enough to hallucinate - it's all inside your own head. It effectively paralyzes you - you go into a "k hole", and you have no clue what's going on in the outside world. I mean, I've taken it and felt like I had a conversation with "the little people" in my mind! But if that kind of experience happened on mushrooms, it'd be profound. On K, it's just a load of fucking gibberish IMO. Oh, and it's addictive (or "compulsive") where as mushrooms aren't in the slightest.
Because it knocks you out (which isn't surprising, given it's used a pre-med) ketamine is profoundly anti-social. It ruined the scene I was part of. Psychedelics opened our minds. Ketamine closed them down again IMO.
But - what do I know - I didn't get really into it (although I took it a fair bit, mostly with other drugs) but others I know did, maybe it did something for them it didn't for me.
I'm not sure there's any evidence that taking it once or twice harms your bladder, is there? I know someone who pisses blood because he took too much K, but he was on it pretty much daily for years.
How do you take it under medical supervision? We snorted it. Under medical supervision, do they inject it? I wouldn't fancy that either, I've never injected drugs and don't intend to start!