I work full time from home, I spend around 12hours a day at my desk sometimes more and staying in good health, motivated and brain clear is an everyday must ! it took time but here is my routine 
- 8h15 am : wake up stretches/light gym moves that are made to enforce my back/arms/wrists ( because I get carpial canal problems and shoulder problems so I need to have muscles there in order to not hurt )
- 8h45: big Breakfast, and I take my time, eat all I want(cofee+sandwich+cheese), read science magazines ( cuz I love science ) and just relax
- 9h15: I finally open my phone and my computer and start reading mails and messages ( I noticed that my day is better if I don't check my phone before being fully awake and happy )
- 9h45 : I go wash up and dress up ( yeah late I know but my body really takes a long time to fully wake up )
- 10 am : I start working, I am an independant illustrator so I draw all day. I always have a bottle of water next to me ( Hydration with simple plain water is the best possible way, I don't like sugared drinks, but teas are awesome too in winter )
- 12 am : I go to lunch, no snacks, cooked food, I like to cook, the body needs everything to be healthy, I don't eat anything special, but food is also part of how your body will be so don't skip meals ! It's also good for your brain, I mean how nice is it to eat a good warm meal right ?
- 1 pm : if it's a beautiful day I'll go biking for a while and if it's bad, I'll either nap or lately I've been into jumping rope ( also good for shoulders )
- 2pm : Back in office and working, I take some breaks, like once or twice but when I'm into my work I just work all day without a stop.
-7.30pm : Diner ( I don't eat much for diner cuz I tend to be fat and as I don't move a lot all day I need to be careful here )
- 8pm I usually work a bit more here sometimes not but I often do these days because after 8 is my " personal projects time " meaning = my comic even if sometimes I start working on it around 6pm if I'm bored of my client work.
- at 10pm max I stop working, then shower, bed and either games or k dramas or us series or a movie, just relax time.
- I try to be asleep before midnight or around midnight if I sleep after I'm very tired for the next the day ( but drama tends to ruin this fine rule for me )
This is for the weekdays, on weekends I just enjoy myself like taking a morning in bed, going out a bit
, enjoying people's company ( cuz working from home is lonely ) and visiting places too if the weither is nice. Not staying home at least, the brain needs air ! Even if sometimes I do work a bit on saturdays and sunday's afternoons...
It took me around 3 years to understand what my body needed to work as much as I wanted and not feel like dying of tiredness ! This works for me and may seem very strict but it's perfect for me. Also I have no kids/boyfriend so I'm kinda free on this ...