I understand what you're saying, but I would rewrite it like this... "It is very important for me to be healthy. If I'm sick, I'm not able to work." or "It is very important for me to be healthy. Let's say I'm sick, I would not be able to work." In my first rewrite, I think I've slightly changed the meaning of your second sentence. When you say "let's say I'm sick" you are implying that there are many reasons why you should remain healthy, but you are about to give ONE example "I'm not able to work". In my version "If I'm sick, I'm not able to work", I'm only giving one definite reason. So if I wanted to give the exact meaning of your original sentence I would say... "There are many reasons why it is very important for me to be healthy. For example, if I'm sick, I would not be able to work."