This is really weird because this is the first time I am hearing a development like yours about coconut water inducing tiredness when drank. The truth is, coconut water is renowned for its property of energizing whoever there drinker is. However, with this your claim, I presume something must be out of place either on the side of the coconut water or you that consumed it.
Notwithstanding, it might be that the coconut water is the type that has its energy-boosting property depleted due to over preservation. Because there are times, I will open up coconut, to my surprise, I will discover the water has gather somewhat unpleasant smell in it. If this is not the case, it might be that you body system is not processing coconut water as other people's body do.
I will advise you seek the help of a professional medical expert in order for your condition to be ascertained. Assumptions are not ideal when it comes to matters of health.