Stop checking Slack and email mid-task. Unanswered messages drain mental energy even when you ignore them. Finish what you're doing first, then respond. Your focus is limited each day, so spend it on one thing at a time.
Chapters
This is what works for me. I try not to read Slack messages or emails while I am focusing on finishing a certain task. A lot of times there will be a response needed and you will want to respond to that message, and if you don't respond immediately, you will keep it in your head, which takes some of the energy from you. So it's a lot better if you just don't even look at it in the first place. Finish the task first, and only after, check your messages, check your emails, and respond to them. So remember, you have limited mental energy every day. Make sure to use it for the right things. What I suggest is to be cautious and preserve it as much as possible. Getting many things done consistently is a lot better than getting a lot of things done sporadically and then needing a longer time to recharge.