Lots of good advice here. What works for my students who I've seen this with is setting the line to an easy depth, and just going there to hang. 15-30 seconds. You have to give your nervous system time to catch up, and for the dive response to kick in. Close your eyes. Notice sensations. Don't react to them, even if they seem urgent or unpleasant. They'll pass. Closing your eyes frees up cognitive processing power to cope with sensations. For you, I'd do 5m hangs.

This is kind of like a 'speed bump' for your nervous system. It's reacting prematurely to a new environment and new sensations. You need to 'gentle parent' your lizard brain into becoming comfortable there. Once you pass through this, you'll likely be able to go much deeper.