He's not arching his tail anymore but he is still curling his skirts upwards and releasing flat, although not as harshly/sharply as before. It's similar to the 'death curl' we all dread but he curls upwards briefly and then releases for 5 seconds.
I'm assuming as the death curl is a neurological condition that the toxin must be traveling through the brain the cause this.
His breathing has settled a little but is still strong ... come on boy, fight it !
Martin