I'm notorious for this.
There are people that do not like me because of this and they do not understand. I will go days before responding sometimes. It is not because of anything other than I got distracted and forgot to respond and my day went on, went to sleep... I respond in my head, but forget to actually follow through with typing it all out! Also, it is because I am a true introvert and I cannot really be, you know, accessible at all times of the day every day so I'll tell myself I'll respond later then forget. :/