Mental Breakdown

Not knowing the particulars, I'd be in the camp of suggesting you pursue that time off. You'd be surprised how beneficial it can be once you're able to have the chance to gather your thoughts again. I stayed the course for 6 years even though I did a self-reflection each year that pointed to leaving for a different profession. In my case, I eventually left (should have done it sooner) to become a software engineer because as a tech coverage banker, I really did enjoy seeing what the clients I worked with were building. I know it's difficult to think about doing something else when the high finance path is nicely structured for us, but there is a huge potential for personal growth ahead when you decide to retake the wheel and figure out what truly it is you want to do. You're in your 20s, this is the time to try things out and not live with the "what if". 

Currently an AN2 at a European IB about to become (hopefully) an AS0 here to say what you are feeling is incredibly normal and you are not alone in feeling this way. About 50% of my grad class had departed after the first bonus and nearly 75% are gone now two months before the second bonus even hits, with the vast majority going outside the PE/GE/HF space.

If you truly hate it and don't see yourself doing anything in this realm again, my opinion is to just let go and quit. If you were smart / motivated enough to get an IB gig, I promise you will never be economically desperate, its just a matter of how much you are willing to grind for huge pay packages in your 20s (which may not matter at all to you).

That being said, if what bothers you about the job is not the hours but not feeling up to speed, then I would implore you to stay and perservere through cause I promise the learning hurdle is very close to being passed!  And also IMO its 10x cooler to exit as a snr ASO/VP from IB/PE into a startup or corporate gig as you jump a few more levels up in corporate seniority (still a paycut but much more comfy existence along with the chiller hours) 

I had a very similar experience back in 2018, although as an AS3. Toxic workplace, long hours, no leadership, pulled into twice as many deals than everyone else but was always passed over for promotion in favor of external hires. I couldn't take it anymore but was too stressed, burnt out and jittery to interview well at other banks. I saved up a bit of money and eventually decided to quit without having another job lined up, and it was the best decision I've ever made. I spent a few months working on my fitness, getting my health back and traveling around the country. Also gave me an opportunity to rediscover my interests and consider a future career path. Four months after quitting I interviewed with another bank and was immediately hired as a VP covering a slightly different sector. I've been there ever since and am still happy with the move. Long story short, your health and happiness should come first and you should trust your gut on these decisions.

Is your family able to help you with living expenses for a few months? If so, give your two weeks tomorrow. Don't even think about your next step for at least 4-6 weeks, just decompress a bit. This isn't as uncommon as a move as you think. You WILL land your next step just fine.

The above advice is right on - you are not throwing your career away whatsoever. The work you've put in thus far enable you to take a step back for a minute and decide what's next. Your banking experience and school will open a LOT of doors for you, even if you decide to take 3-6 months off to recover. 

There are better jobs out there and teams that will value your experience and treat you right.

Sorry to hear, brother.  If you think (a) you've been doing good work, (b) the company needs you, or (c) the company HR/higher-ups are kind people, you could instead tell them that candidly, you're on your last nerve and about to quit. 

They are likely to offer (and you may want to accept) a two-month sabbatical or something like that.  A short (one/two week) vacation won't really help.

As others have said, if needed, please do quit and take some time to yourself - I'm sure you'll do really well. 

Take a week vacation and go to the beach. Book a session with a therapist at the beach.

Go to your staffer and tell them you need a mental break now. They will accommodate you; we no longer live in a world where these feelings should be the norm.

I was in MBB and had a similar experience. It took almost a year to recover burnout wise, and this was after exiting to a very well known tech firm with laughably excellent WLB. In hindsight, I stayed too long, a huskless robot going through the motions fueled only by the vestiges of drive I had during the beginning of my stint. 

I will say this from experience, knowing how dark and hopeless things seem. Hang on, things WILL get better. This will be a blessing to you in the future when you face lifes future career struggles and laugh, knowing you have already experienced the worst it can offer.

Alternatively, there are NO downsides for you to quit now. seriously. One of my best friends burned out of his banking firm in 3 months and found a job after a few months. I had another who was forced out of our firm and she landed on her feet. I have yet to see a single friend unemployed for more than a few months after quitting a BB banking or MBB consulting job. When I was applying to places, I literally cold applied and still got interviews

Well I hate to be the one to say it but a therapist probably can't solve this problem for you. Some people here seem to think if you're doing what you're supposed to be doing, grinding 80+ hours a week in a bank, and you're not happy you need to see a therapist to fix it. If there's a legal problem with the deal you need to call the lawyers. Give me a break. You need to take a minute with yourself, and decide if you want to do this or not. It's your life and you don't have to. If you don't want to, then every day you spend at the bank is a waste of time you could spend doing the next thing. But if you do want to do it, then you need to design a path for yourself that you can be happy with. Maybe you apply for an MBA, put an end date on your job, and explore some other options in finance. Do the math, how many analysts and associates are there? How many of them are still going to be in banking or pe in 10 years? It's an up or out game, and there are people that are loving it. If that's not you, then find an exit before it starts to feel like a squid game.