i don't worry at all about tomorrow it's what i can and can't do today that bothers me --- whether this is right or wrong depends on experiences - when that car pulled out on me all those years ago i should've been dead - losing blood etc........ but i was having a laugh with the doctors and stuff really didn't bother me that i was at deaths door, i'm not scared of dying.
But what if, today, you were not able to train or compete because you messed up your leg beyond repair? Tomorrow will become today whether you like it or not. If you don't want today to be full of regret, you need to be careful not to over do it and make bad worse. Do you think, if you had been crippled for life in that car wreck, you would enjoy today as much as you are enjoying it now? You didn't have control over a car wreck (presumably), but you have control over your physical well being today.
As an aside, time is an illusion. It's always now. It's always been now, and it will always be now. But now changes. Make sure it changes for the better, and not for the worse.