In gambling you only win from the start then you lose whenever you win a certain amount.
Gambling can't e considered as a sickness as it is a type of entertainment,
Addiction to it can be considered,
But only if that addiction do cause a lot of negative effects on the life of the gamblers,
Addiction in gambling are not that severe in comparison to other addiction, so For me, I don't consider it a sickness as long as it does not have any negative effects in your life.