Thank you everyone for your contributions. I've spotted and upvoted some very good answers. If anyone has more tips and tricks please chime in.

Some takeaways so far:

  - work schedule: do 1.5-2h blocks of work alternated by 0.5-1h blocks of non-stress activities, OR blocks of different types of work.
  - eat healthy
  - get enough sleep 
  - exercise
  - meditate
  - alternate sit/stand posture 

Also, since a lot of you are asking, I thought I'd provide more context. I'm the founder of my current startup. My background is software engineering. Love what I do, love my team. I do prioritize my tasks. "Hacking"-wise, I've been doing meditation, eating very healthy (organic, lo-carb, no-caffeine, no-drug), exercising. I can usually bump to 60hrs if I do what I'm experienced with, but things seem to come to a limit of 45hrs under stressful periods.

Thanks to your answers, I now have some ideas of what to fix:

  - sleep: my total sleep hours is fine, but my sleep schedule is wild.
  - work schedule: gonna try balancing the work blocks with relax blocks. I usually get stuck on the computer coding for 3 hours straight. Will have to learn to leave it after 1.5-2h.

So far so good, thanks everyone! Remember to chime in if you have anything else to add.