you need to take breaks, yes diet is important, sleep is important as well and good health/nutrition, there are no distractions in my studio meaning no mobile phone, no email checking, and no internet when I am actually mixing a track until it is done, I tend to work for about 30-40 minutes and have a 10 minute break for my ears ideally in total silence then go back to it, I also do not mix loud and often in mono, it always gets better in stereo when it sounds good in mono.