Once you are in a cycle of negativity, it is so hard to get out of it because the whole reason you are in a cycle of negativity in the first place is because you have lost awareness of what is happening. Any desire can send you into a type of addiction, and when you loose awareness you will come to rely on that positive feeling to make you happy. Eventually you might come to the stage whereby that is the only thing that is sustaining you, an empty shell. In Thailand a guru I once met told me “control your sexual energy”. At the time this was not a major feature in my life as I was preoccupied with travelling and in a relatively mindful state. Little did I know that in later times of turmoil this would be one of the things I would turn to as a distraction from my states of mindlessness. The more you indulge in various pleasures as a means of escape, the more you increase your addiction to them, no matter what it is. It could be something as simple as watching TV or going on Facebook, or it could be something as serious as a drug addiction. Usually the greater your state of inner strife, the greater the thrill you seek in order to escape. There is absolutely nothing wrong with enjoying something pleasurable in life, but when it becomes a means of escape then you will find yourself in a negative cycle soon enough. The reason I call it a cycle is because the more you indulge in it, the greater your anxiety becomes and the more you indulge in it to escape. I remember that I was naive enough to think that I would be immune from this process somehow. Then finally when I am in the midst of a (relatively small) slump, I find myself making excuses to meditate later, be mindful later, and my ego grows and I need a lot of strength to drag myself out of the self -created hole of negativity once more. People around you will be affected negativity by this as well.
So in summary, there is NEVER a time when you should make exceptions for mindfulness, and you should endeavour to recognise the signs of a negative cycle as soon as possible.