I need a script!!!

[V-Man]

Unfortunately, since the damage screen only shows up if you've received damage, this is not very reliable.
[cubescript]
damagescreenfade 1000
damagescreen 0
bind s [-= fov 15; damagescreen 1; onrelease [damagescreen 0; += fov 15]]
[/cubescript]
The damagescreenalpha value is left to your discretion, though I'd imagine you'll want to hone it to a really comfortable level.