Can confirm from personal experience. Even a lot of vipassana meditation by itself can send you into psychotic states when you're not ready for all the insight yet. I came very close to psychosis once, experienced ego death, broke down mentally and had to spend 2 months in a depression ward. Cannot recommend.
'ego death' can be really scary at first. There is an entire article in wikipedia about it ( https://en.wikipedia.org/wiki/Ego_death ) and how to integrate such experiences.
I attended a 10 day course earlier this year. Before I went, I had read these stories, and admittedly, I was afraid I'd, at the very least, be terrified by what came up in my mind. But that's not what happened. Following their simple instructions, my mind became quieter, calmer, and sharper. I had more control over my fear response. It ended up being a great experience, and I'd recommend anyone interested in one of these courses to go for it.
I was also concerned about the environment. I was thousands of miles away from anyone I knew in a strange place and different country. We were asked to hand over our phones, reading material, journals. We were asked not to speak to anyone and to avoid any form of communication. But this was all to benefit our meditation. We were given a space for several days to really focus on ourselves without external distractions. The day our silence was lifted, you really got to experience just how much talking to another person can disturb/distract your mind.
And it's not torturous at all, I and multiple friends have attended it. My 60 year old parents have attended it. They charge no fees, in fact you can only donate(optional and they won't even ask) if you have completed the entire course. You are free to leave at any point of time, no questions asked.
Vipassana meditation is a powerful technique though. They clearly mention on their website asking people to stay away in case they have any latent mental illnesses. Though the number of positive experiences does outnumber the negative ones ( https://www.google.com/search?q=vipassana+positive ). I've seen people cry after a meditation session because it helped them release energy inside them which they didn't know was stored.
Allow me please to ingratiate myself with pity. I know exactly what sort of (negative) energy I have pent up in me.
Resentment.
I get triggered for being short-changed a penny just as much as being robbed of of hundreds. I boil to illogic, stammering incoherence when I see injustice against my fellow helpless. I foam at the mouth with silent trembling rage when after borrowing money to put food on the table I see the corrupt fat cats get away without paying for crimes of fraud, of tax evasion and unfair commerce. I spin in dizzying bitterness when my honest work, my products, my services are overlooked for incompetent, more expensive and even non-existent alternative deals done with buddies and the small-time mafia-wannabe (rigged tenders). I am maddened with incipient indignation when I find out that my seemingly legitimate medical insurance claim was denied on a technicality in the small print. I jump at the chance to chastise anyone over zealously, anyone who's nursing the erroneous thought we live in a meritocracy.
I am resentful. That's my pent up energy, right there.
I have tried meditation. Believe me. I've read over the years through a calm eye and an at-ease mind the Buddhist teachings of compassion. And I think it is all a lie. You cannot sell compassion to the poor. To the strugglers. To the down-trodden. To the have-nots. That would be Jesus and his religion all over again.
I agree with you. Maybe what you need is to accept that other people will often be jerks when they can. It's like bad weather - you suffer the consequences but you can't change it. So why be resentful at something that is like the weather? That's what I am telling myself, to keep calm.
There are also 1 day / 2 day / 5 day meditation retreats for those who are looking for something less intense. Still can be great experiences. I once did a 4 day retreat but left after the 3rd day because I felt good and like I got my dose of whatever I needed. I would say aim for consistency rather than intensity.
Another thing to note is you might need to account for integration time after the retreat.
looking through the links and experience from forum posters is scary, vipassana and similarly intense experiences like high dose psychedelic induced ego death can have similar results. the minds of mindfulness beginners when in next level introspection are scary