You avoid it. How? By having a clear plan and having decided ahead of time what's important. Many entrepreneurs, especially those without a lot of experience at it, confuse hyper-activity with progress. Don't do that. Drive your own activities, gauge each thing you do against it's impact on making the future you want happen - and most importantly, say No a lot. Stay focused on impact and remember that all urgent things aren't actually important things.
Great answer by Stuart. I would also add that you need to know WHY you are doing what you are doing. Your why is critical to not getting burned out. When your business centers on why you opened the doors in the first place, what problem you are solving and is about more than a product/service and customers, that's when you don't have to worry about burnout.
I've been here.
Turn off your phone, don't use facebook and take 3 days of rest. Full rest.
When you come back, make sure push notifications from facebook, twitter, etc are OFF. I know it's tough, even if you use those to get business. But do it. It is more of a drain than you think.
Most importantly, find your 20 mile march. A small set of actions you can do each day to lead to your bigger goal.
For more on the 20 mile march, watch my video or reach out! I would love to help. Hope you are pushing through this.