I own an e-commerce consulting firm with my husband and every time our future looks stellar, the workload becomes unhealthy. My husband put in 60 hrs already this week training new hires by day and working on client solutions by night. This is normal. I don't want to be flippant, but welcome to the world of business. But you must take care of your body.
Energy wears down because the body gives out before the work does.
Hire more people, and let people do more for you. In one case I actually work with an internal writing group where the writers are unfamiliar with many of the tools that I use. Originally, I began teaching them so that they could do their jobs more effectively. Now I have reason to believe that one of the writers is trying to learn all that she can from me so that she can start a competing business. I also regularly get asked by former coworkers and associates if I can find work for them.