As my boxing gym likes to advertise: "Stressed? Come punch a bag"

Running helps too.

My recommendation for external things: Make a big overview of all the things you have to do (Big mindmap for example). This reduces uncertainty, which causes stress. Then prioritize the responsibilities. Make a plan of action, and execute! :-)

My recommendation for internal things: Take breaks, your mind needs rest. Ever needed a solution for something, went to sleep and woke up with the answer? Your brain is working when sleeping and resting. Get enough sleep. Eat good quality food. Drink enough water. Exercise 3 times a week.

Oh and once in a while treat yourself to a visit to a spa or a massage or something you will enjoy and relax you totally. Good luck!

take a break, write the problem down and make a list. do something fun. return to the list, scratch out all unimportant stuff and get a bit of momentum going.

Is taking a day off an option? I can definitely relate to that, there are days that everything seems overwhelming but then the next day it doesn't look that bad. I guess our brain really likes to fuck with us sometimes.

If I'm not in the mood of solving problems, I usually let it go for a while, eventually things start to get easier to deal with.

Meditating and some form physical activity helps in feeling upbeat. When mind gets really anxious, getting out and going for a short walk helps.

All great answers - I'd just add to remember that often the pressure to get everything done at once comes from yourself not outside. Things can be prioritised, deferred or outsourced. Short term definitely take a break and clear your head, longer term perhaps think about what you could automate, pass to someone else to do - or just stop doing altogether