When you start to feel that knot in your stumic or feel like you're going to be sick those or also signs you need to stop anything.
But in the rush of chasing losses or with the excitements from gambling, almost every gambler will be failing to find out those symptoms of getting sick. If it is not so, there would have been many profit making gamblers on regular basis.
True, chasing losses is worst enemy of gambler, because nobody is chasing loses with small bet, usually with larger bankroll and higher bets, and only rare players can win in those situations.
Failing to stop gambling just after made some profits was my one of my prime reasons for I am not becoming a profit making gambler till date.
Well, you can always withdraw half coins(or more) and continue to gamble with other half, and when you lose don't deposit that other half.