There is no way to sugar coat this. If you work in a startup, you will get burned out. A lot. And often. And probably a few more times after that. And then one more time.
And I have no sympathy for you.
The reality is that burning out comes with the territory. If you chose to work for a startup, you're going to get burned out or you're probably not doing your job right. It is inevitable. During the early days of a startup, you and your coworkers will live in a constant state of burnout. It's the only reality you will know, but you won't really care because everyone is in the same stressed out boat. You will all be tired, angry, poor, and drunk, but it's okay because the adrenaline and hope will keep you going.
Honestly, it was my favorite time working at a startup. Those were the good old days.
But as you start to hire more people, the burnout becomes less and less a part of your daily routine. There will be more people to take some of the responsibilities and lighten your load, but there will always be a lot of work to get done and more problems to solve no matter how big the company gets. Having more coworkers won't erase your likelihood of becoming exhausted and worn out.
Becoming a burned out employee is disruptive to yourself and to your company. I've seen people leave their company because they were burned out and couldn't come back from it. I've seen people ruin relationships with coworkers because they were burned out and acted poorly. Everyone shows the the symptoms of the burnout differently, but it always costs the company a lot of time, money and energy to rejuvenate an employee. I can't prevent you from ever getting burned out because sometimes it is a necessary evil to get the job done right, but I can help you learn how to do it less often.
My one and only rule for not getting burned out is simple.
Get over yourself.
I hate to be the one to tell you this (just kidding, I love it), but you are not that important. The company will not fall over and die if you choose to not answer an email while you are having dinner with your family. It's completely in your control to avoid the burnout. I literally have zero sympathy for people who get burned out because I know that they are doing it to themselves. If you need to take time for yourself in order to not become drained at work, then take time for yourself. It's that simple.
No one is standing over you at 12 AM making you answer emails. No one is telling you that you can't go for a run in order to save your sanity. These are your decisions and you have no one to blame but yourself.
So stop complaining about how you are "so busy" and your boss is working you "too hard" and you are "so stressed."
You work in a startup, Captain Obvious. Get used to it.
There will always be more work to do and it will all still be there after you eat lunch. You can't wait for your boss or anyone else to tell you to take a day off. Of course, there will be certain times that you need to work late and take care of something urgent, even when you need a break. Make sure you have at least one person from work that you will respond to at anytime so you know if something important comes up, but then let yourself ignore everyone else. It can be your boss or a trusted coworker, but learn to prioritize people and situations so you don't always have to go at the same high speed.
Bottom line: There will always be times in your career, especially in a startup, where you will get burned out. But learn to do it less often by taking care of yourself when you need to. Don't wait for someone else to tell you to take a bubble bath.
Because they won't.
And if they do, that's kinda creepy. #justsayin