That sounds like an absolute nightmare.
Is your management chain aware that you are diagnosed with ADHD? Staying off Slack should be considered a very reasonable accommodation for your condition. Perhaps go ahead and do it, but also tell them why, and how it will improve your productivity.
Alternatively maybe it's time to look for a different job with a more appropriate working environment, one that doesn't lead to such stress. How have you found previous jobs, in terms of being able to focus?