I know what you mean. The more you do achieve, the more you have to lose. I can remember also feeling fear alongside the very few times I've felt happier in life.
Whether it will be worth it, none of us know. We don't know whether we'll get what we're trying to attain. We don't know whether it will feel worthwhile enough if we do. We don't know whether we'll lose it all ultimately.
I suppose all we do know about is the present moment and perhaps the near future. Would it feel better to stop trying now or would there be some regret in the near future that we'd just given up? I suppose I feel like, so long as there's some hope, there's still some motivation to try.
The other thing is practicalities. Personally, I don't feel like I can kill myself at the moment- I want to wait for my Dad to go first. So for me, that means finding the easiest path through life while I'm stuck here. My creative job has always been pretty much the most important thing in my life. So- while it's full of risk, it's hard work, it can be stressful and it invites in plenty of scope for failure and disappointment, it's still the lesser of the evils for me. So- I pursue it and I do other things I actually hate to ensure I'm fit enough to do it- like exercise. I think it's just making an assessment of our options and going for the one that suits us the best.
As to whether we could fail- sure we could. Any kind of calamity could befall any of us at any moment but- probably better to not worry about stuff that hasn't happened yet. (I'm like that too though. I tend to catastrophize over every possible bad thing that could happen.) If bad stuff does happen, we'll have to deal with it at that moment. I suppose it's more at that point where we'll really decide whether we want to keep fighting or whether we've had enough.
I'm guessing how tired you felt hasn't helped matters. I hope you feel more able to cope after some sleep.
. U r doing great though u have a lot to live for 
