I worked for a call centre company which was bought out by another call centre company who are pretty notorious for not being a great employer. I'd already been feeling unhappy with where I was, but things had actually improved slightly for a while.
Then they decided that my team, who were all tenured customer service agents, were going to be pulled from our current campaign and moved over to sales. They kept pushing the big bonuses we'd be able to make there and what a good thing this was.
I went into the training and could see straight away that it was not going to be the right environment for me, so I immediately started making applications for other jobs and polishing my CV. They went easy on us for about two weeks and then started putting the pressure on for making more sales and getting add ons when we did get a sale; one person got to the point that they were actually hitting their sales targets but got put on a PIP because the increase in sales meant their percentage of add on sales fell, so their job was going to be at risk basically because they had managed to hit their sales target.
It honestly felt like they knew we'd all be entitled to significant redundancy pay if they let us go (none of us had been there for less than 5 years; I'd been there over ten) so they put us into something we wouldn't have chosen/wasn't suited to our skills and then let us either walk, or would ultimately be able to let you go for not achieving the set targets.
I'd been unhappy with the way things were since before the change in ownership, but that change made it feel a more toxic environment and then the change in campaign tipped me over the edge. I knew I either needed to get out or I'd end up signed off due to my mental health.
I worked on the basis that it's easier to find a job when you still have one (you still have that monthly income, so you're not at the point of taking anything that comes along just so you can pay the bills). I worked on interview skills and sorted out clothes I could wear to an interview and was lucky enough that the right job for me came along.
Had it not, I would've ridden it out for as long as I could, but I know my mental health was slipping and I likely would've ended up needing time off to give myself a break.
I'd say, stay with the job for now, things might improve and you might decide to stay, but in the meanwhile, work on your exit strategy; put out feelers for jobs you could do, work on your CV, practice what you'd say in an interview, make lists of your transferable skills, etc. It definitely helped me feel like I was doing something even when I felt totally stuck.