Guys, i am having a tough time in work. So, i am sharing the story and questions here-

Initially, i was doing well with new projects and other existing projects where implemented new features.

But recently, i am assigned to a old project created by clients and some senior developer worked on it .

Ps: I was also assigned to this project 8 months earlier but was reassigned to other projects.

Now, Our senior developer who worked on it resigned because of the messy project and a lot of pressure from boss.
my colleague also resigned because of this.

Due to this, all this pressure thrown upon me. I am working on it relentlessly but i am soo burned out that i am actually feeling sick and constantly having headache.

And main thing is that the project has so many errors which iam getting during testing and i have to fix all of the error.
And yes they have documentation but shitty unreadable documentation . My manager also rebuking me why i dont remember things said to me 8 months earlier. (That time i just joined the company)

I don't know what will happen to me if i cant tackle this project.
And what should i do in such cases as my mental health is deteriorating day by day.