I usually have about 3 or 4 plates spinning at once. Burnout really isn't an option for me, but it happens from time to time. There are two things I can do about burnout:
* Take some time off
This is my preferred option but isn't always available. My family has a small home on an island in the mediterranean, I try to make sure I go there once a year. I take no laptop and my phone is off (save a check-in at work once a week). Last year I reneged slightly on my tech ban and took an ebook reader (as it was easier on the baggage than taking a load of books) - it nearly paid for itself on that holiday alone (I got through 11 books in 14 days).
* A change can be as good as a rest
I do all kinds of things to take my mind of the thing causing me stress. I cycle, I learn how to make cocktails (although that doesn't help the burnout if I overdo it!) - at the moment I'm writing an old school demo for an 8-bit computer to help me with a private conference I'm organising.
I've had serious burnout a couple of times, mild burnout normally kicks in once or twice a year. Stress is an absolute killer, so I'd recommend that anyone facing burnout does everything they can to keep stress to a minimum. Burnout is nature's way of telling you to stop for a while, or at least change direction (in my experience, YMMV).
The key for me is one real, full day off. No work, no half-day, etc. I've found that not taking any days off is what burns me out more than anything. I probably put in more productive hours taking off one day per week than I did during all those years when I tried working every day as long as coffee would keep me going.
I'd like to say that I take off one day every weekend, but that would be a lie. I probably take off one or two Sundays a month, but I do them completely without even responding to work mail, and that seems to be enough.
Like the other commenters, though, I also keep up working out. But that's worth doing just to improve your sleep -- I find that the better sleep more than offsets the time spent in the gym.
Sometimes when I start feeling burned out I just take a couple of days off from startup work (I still work a dayjob though) and when I get home from my dayjob I go watch a movie (living across the street from a theater helps), or read a novel or something, instead of working. And now that my knee is almost healthy again, I'll be getting back into working out regularly... I'll start lifting weights and doing some trail running and mountain biking soon.
Other than that, hitting up the occasional concert and jumping in the mosh pit is always a good stress reliever.
Edit: Otherwise it depends on the situation. Different situations have different options for taking time off. Different situations have different demands. Are you burnt out from a month of doing nothing but working or from 10 years of doing the same things?
Ideally you would just have a decent life balance and if you don't have that then figure out how you can bring that back.
I listen to my favorite music (Mozart for me) and play some sandboxy games like Minecraft and GTA. I just try to forget about my startup for the evening and then get a full night's sleep. That always makes me feel refreshed.
* Take some time off
This is my preferred option but isn't always available. My family has a small home on an island in the mediterranean, I try to make sure I go there once a year. I take no laptop and my phone is off (save a check-in at work once a week). Last year I reneged slightly on my tech ban and took an ebook reader (as it was easier on the baggage than taking a load of books) - it nearly paid for itself on that holiday alone (I got through 11 books in 14 days).
* A change can be as good as a rest
I do all kinds of things to take my mind of the thing causing me stress. I cycle, I learn how to make cocktails (although that doesn't help the burnout if I overdo it!) - at the moment I'm writing an old school demo for an 8-bit computer to help me with a private conference I'm organising.
I've had serious burnout a couple of times, mild burnout normally kicks in once or twice a year. Stress is an absolute killer, so I'd recommend that anyone facing burnout does everything they can to keep stress to a minimum. Burnout is nature's way of telling you to stop for a while, or at least change direction (in my experience, YMMV).