It sounds more like a panic attack, but yeah, it's still a difficult thing to deal with. People with undiagnosed ADHD tend to have tendencies towards anxiety and depression. I've been experiencing extreme anxiety attacks after taking my meds until I switched to non-stimulant ones, which have eased my nervous system, and now I don't experience anxiety as a result!
And when it comes to dealing with panic attacks before, for example, presenting a project, try first to find a calm place where you can focus on your breathing (5 seconds inhale - 5 seconds hold - 5 seconds exhale - 5 seconds hold); try to name 5 things you see within your field of vision, then 5 sounds you hear, and maybe even try to distinguish 5 different smells :) Focus on the sensation of your clothing against your skin and keep breathing. Locate where in your body the feeling of anxiety arises (usually in the chest) and imagine mentally reducing that sensation to the size of a matchbox and tuck it away there. If possible, apply a pack of frozen peas (or any other frozen item) to your chest - it quickly calms the nervous system. You can also hold an ice cube in your hand. And when you start the presentation, begin with a small joke to lighten the atmosphere :) After the first slide, as you get engrossed in your storytelling, anxiety will naturally subside!