You need rest days! Yea, I said! Two of the most dreaded words in a "gym rats" vocabulary. But guess what? Rest days are not only important for your physical well being but they are good for your mental state as-well. After a few really tough workouts your mind, body and central nervous system crave deep sleep, water, macro & micro-nutrients (protein) and rest so the body can repair and rebuild damaged muscle tissue. If you fail to take the appropriate rest days that your body needs you will slowly break down and get injured — and when that happens you'll be useless and depressed!
Everyone is slightly different so rest days or weeks should be spaced differently. But my rule of thumb is if you train 4-6 days a week — then every 4-6 weeks you should take a straight 4 day rest. And by rest I don't mean sit n the couch (although that would be ok for some), I mean just walk, hike or bike, but no training with weights.
The holidays catch a bad wrap because we all sit around and gain lots of weight but I actually see them as a blessing for many. Most of us are addicted to our workouts (me included) — so when you're "forced" to sit around for a couple of days and eat and drink pretty much whatever you want, the holidays force your days off. And the myth about gaining a ton of weight is bogus - Yea, I know many of us can pack on anywhere form 2 to 10 pounds in that month span but within 3 to 5 days of regimented training and eating clean again you can drop that and continue on your health journey.
So in closing: Training hard is important but that doesn't mean you have to puke after every workout. Some of your training should be movement based with lower volume and lower intensity. After those brutal tough training months, take a week off and train for the long haul. Now go kick ass (and take some days off)!