Being a designer takes a lot on your mental AND physical health. You stare in front of a screen for hours a day, losing track of time to go to the gym or clean or eat a decent meal, just to get criticized on all the work you frantically put together before an absurd deadline. Then you are distraught causing yourself to be unmotivated when they scratch the whole design and go with a stock. On the other hand, designing can be the most invigorating muse when you are in a flow and ideas just come to you and the work you turn in gets praised and pat on the back causing more inspiration to flow and keep the high time worth the low. Although it's extremes like this that can really take a toll on a designer's mental and physical health.
You have to stop once and a while to Sharpen the Saw. A designer's best asset is themselves, they are the container for their creativity. You may feel like you don't have time to do things like get good sleep, eat good food, and exercise when in reality you don't have time NOT to do these things. Take some time out of your week to meal prep for a few days so that you have something quick and prepared and aren't reaching for ramen or microwave chicken nuggets. Make it a priority daily to do something active, it doesn't have to be the gym. Have a morning or night walk by your home or do some yoga in your living room. Also, you get more done in a shorter amount of focused, RESTED time vs being fatigued up all night.
Your mental needs some TLC as well such as sipping a hot cup of tea, taking a nice bubble bath, binge watching your favorite sitcom with girlfriends or watching sports out with your guy friends. Every one deserves some down time from work. If you have a strong foundation, then you will never crumble, even in the worst weather.