I am a big believer that you need to always be out and about in your networking efforts.... but sometimes you just need to skip a night. On occasion, just give yourself a break.
I usually counsel people that if they sign up to go to a business event they need to go, even if they have had a long day and are tired. There is always an excuse to skip your necessary networking, and once you get there you will usually find it worthwhile.
However, sometimes you can just take a pass. As long as you do not make it a habit, from time to time just say "No". Go home early, have some wine (or hot tea), put your feet up and relax.
As long as this is not your habit, you do deserve to take a break from time to time.
Have A Great Day.