Confused and scared

Yeaterday I sat in a theatre bar and signed a contract, I filled out my emergency contacts and a P45. I went on with my first shift and by the end of the night I was at loss to understand why I cant do things as well as others. Simple tasks like sweeping,mopping, bending, carrying, I seemed to struggle and exhaust myself.
Now I understand that what is causing it but what confused me was why it was affecting me in such a way. Last November I collapsed which started a long chain of Hospital appointments and numerous tests. Ive been told that it will be hard to have children, my heart isnt in the best condition and that there is some sort of growth that needs more investigation. I had trouble with walking and doing things people consider normal like tidying or sometimes my chest was hurting while I was bathing. But then the doctors perscribed me some pain killers that seemed to actually be working and although the problems were still there I didnt really experience the pain that went with it.
Doctors had said that I was not fit to work, but I felt great so I when a friend offered me this opportunity I said yes straight away. So again yesterday I filled out all the appropriate forms and started my first shift. Anything they asked I said yes, any questions I answered, but then it got hard. I assisted in hanging 2 different backdrops, moving a table, a rack, chairs and having to sweep. I took my painkillers and while I sat and watched the second part of the performance I thought I was having a heart attack, I was about 5 seconds away from running out of the performance and collapsing again. After that my chest ached, my head thundered and my eyesight blurred. I stuck out the entire shift and have another shift tonight. Now do I do what my fiance and family want me to do, and to give up before I seriously hurt myself and make my condition worse, but at the same time earn money to help pay my bills, or do I carry on and dissapoint my friend who hired me in the first place and mess with the new rota, causing people to work extra shifts to cover the ones I backed out on, but risk making myself worse. This may seem like a simple question to you, but if you have ever been in a situation where you literally cannot afford to buy a loaf of bread or just a bottle of water you may understand the constant debate that goes on in your own head.
Not working, not being able to go for a walk or even just buying something eat makes me feel like a failure and people love to look down on people who cant work. I have lost count of the amount of times people have asked me what I do and then frowned at me smiled politely, walked away and began telling others how they 'loathe people who just cant be bothered to get off their backside and do something rather than scrounge off of other taxpayers hard earn money' . How can I not work? I have to, just to stop other looking down on me, telling me that I cant spend my life doing nothing. I cry from pain ,even thrown up because of pain, sacrificed things I love, spent countless days sat in hospitals while cameras looked at my insides, having blood taken ,being hooked up to machines and quite honestly feeling alone and scared. How do you say that to somebody, how can I stand there and spill all this to someone without sounding like I am looking for sympathy? I cant. People just automatically give the reply of ' oh god' , ' aww thats awful' and feel sorry for you. Likewise how can I tell people that I probably cant have children? I told one person and they looked away and said ' you can adopt' then went on to say how terrible it was that it happens, how woman feel like they have failed if they cant procreate. Obviously thats what I wanted to hear!
I dont know what the right thing to do is im utterly confused. I realised on that first shift that maybe I cant do what everyone else can anymore. I have to be careful but what can I do when I need food?