Firstly, I think you need to slow down, relax and concentrate on the main issues here.

We are all expected to be flexible as regards working hours but once you start staying in the office after 5 or 6pm, there will be repercussions on your personal life and obviously your health as you have mentioned.  Personally I could not keep up that pace.  I like to be busy but not put under that kind of pressure.  My health is extremely important to me.

I just wonder how individuals were able to contact while you were off sick?  and more to the point, if you were off sick, why did you respond?  Lessons to be learned.

Forget looking for another job for now, you have to focus on what you can do to get your health back and then ascertain what can be done to alleviate your heavy workload.  A doctor's line outlining your illness should have alerted HR and your boss as to how your health has deteriorated, which I hope improves soon.

Pneumonia is not something you recover from in a week so consider a further sick line from your doctor until you have fully recovered.  In my company we have a "return to work" interview if we have been off sick and this is conducted by a line manager.  I would suggest on your return you seek a meeting with HR and/or your line manager to discuss your situation - that cannot and must not be ignored.  Only then will your line manager be able to delegate work accordingly.

I am of the opinion if your workload continues at the current rate, you are always going to feel under pressure and your health will suffer.  You also have to learn to say no, sorry I can't get to that today, but I can do it for you tomorrow.  If you are not paid overtime or contracted to work flexi time, then just work your normal hours.  This should be acceptable during your "return to work" period and should be re-assessed on a regular basis by HR and/or your line manager so that your health does not suffer again.

I am sure others will add their comments but you must deal with this in steps to achieve the end result.