Just because you didn’t workout for a few weeks don’t go back to the gym and go hard right off the bat like you haven’t missed a beat. You’re just asking for injuries.
These injuries can be immediate or delayed. If delayed, it means you think you got away with it, but few days later you don’t know why your knee hurts, or why your back hurts.
The few "hard core" workouts you execute right off the bat will not make a difference to the results you’re after other than increase your chance of injuries. Come back into the game steady. Do half of what you would normally do before the holiday break, then slowly build your way up from there every other day.
What will make a difference to getting and keeping great results is your regularity and consistency in working out, not your "one-hit-wonders" here and there.
Let’s put it this way, your workout regime is like being in a relationship. You can’t just start and stop; you can’t expect to spend the next few weeks showing your partner your respect and affection and then stop just because you got lazy. The relationship won’t last the test of time. Even if it does, it won’t be a truly fulfilling one.
This is the same with your workout regime. It can’t be a temporary thing. If you choose it as part of your lifestyle, it only works best when you make it a permanent thing.
It doesn't have to be hard core, it doesn’t have to be everyday or all the time. Just be regular. Be consistent. Even if it’s twice a week, this is more effective in producing long-lasting results than if you were to spend only a short period of time (few months) working out hard 4-6 times a week.