When the cat's away, will the mice play??

So, I had to take my first day off from school last Monday. It was the 10th day of school for us. I hate missing school this early in the year and in general. I am one of those teachers who leaves meticulous plans, very detailed, specific plans. It takes me A LOT of time to plan my lessons when I am going to be away. Sometimes you don't know if you are getting a substitute that really does a great job, or one that is inexperienced or new to your school and its routines and procedures. One thing I always wonder in the days leading up to my absence is should I tell my students that I will be away.  Is it better that I don't tell them so they don't get excited when I'm gone and let the sub really have it? Or, should they just be surprised the day they don't see me? Which is better? I guess I could ask them. Never really considered that. Most of the time whether I tell them or not, they make me proud by making good choices and getting the work done that I have left. What is your philosophy on telling your students that you will be away? Also, do you have a go to plan so that it doesn't take you hours to plan for your absence?