I'm a manager, for a large company.
It's difficult managing staff and operations, and of course being a manager I have to make sure all our work gets completed in a highly stressful environment. Managing staff and absences is difficult, as of course when your short it puts pressure on the other guys, and adds to the stress.
However, there is nothing more important that your health, whether it's mental or physical, as a manager I care more about the well being of my people than the work, at the end of a day a job is just a job, as a manager and a representative of my company I have to ensure that you are being looked after. The work will still be there when you get back, your manager will manage somehow cos thats his job. Please do not worry about work, worry about getting youself better.
Take him up on seeing HR as if they are a big company they will have a big support network, and they will also adress whether you have too much work, or unrealistic objectives. it's not about trying to get you back to work, or fire you, it's about the legal obligation to take care of your well fare.
Don't worry about work, stress is an illness, I know, I suffer with it. You need help on learning how to deal with it.