Cycling into tunnels with claustrophobic person you are cycling in pair
you may need to travel through tunnels (lenght can vary from few hundreds meter to about 7 kilometers)
your travelmate is claustrophobic, therefore tunnels are a challenge for him
avoiding the tunnel is not always a practical option (it may need a 50 km detour)


Under these conditions, which would be the best approach to prevent as much as possible issues like panic attack, irrational behaviours etc.?
This is how we did it, for all tunnels longer than 150 meters (ranging from 200 meters to 4 km):


before the entrance of the tunnel, the leader slows down or even stop, allowing the follower to get closer
after entering the tunnel with lights on, regardless if there is a cyclable sidewalk or not, every once in a while the leader ring once his bell
if the follower feels ok with the leader's distance/pace, he rings back once. Else, he rings back twice. The follower can also ring twice whenever he feels he should get closer.


The benefit we got:


no need for the leader to turn his head and look back
the follower feels actually in control and not left alone