It was probably a side effect of overusing his Mangekyou Sharingan.
Sasuke stated that every body cell hurt while using Susano'o, by that time, Sasuke only had a humanoid incomplete skeleton version.
You must be registered for see images
Itachi already by that point mastered his Susano'o to his limitations.
You must be registered for see images
It seemed like asthma in the flashbacks. Stress and depression due induce that.
Do you have any scans? This would be very useful information.
I will post them tomorrow.
