Your physical condition might not be your livelihood, but it is one of your keys to a good life.
You need to make like Whoopi and get back in the habit. Here are a few strategies:
1. Do something completely different
Earlier this year I was burnt out from barbell training. For four weeks, I switched exclusively to kettlebell workouts. Rather than 90-minute powerlifting sessions, I did 20-minute ballistic complexes. I hit it heavy and fast and then got the hell out. I did this in my basement or garage. Usually without pants.
It doesn't have to be as drastic as completely switching modalities. Use a little specialized variety, a.k.a. "the same, but different." Accustomed to back squats? Do front squats. Do you deadlift with a conventional stance? Use sumo.
Another great idea: do everything unilaterally (one limb at a time). Here's quick sample program:
A1. Goblet reverse lunge x 15/side
A2. Single-arm overhead press x 10/side
A3. Single-arm cable row x 6/side
Choose weights that feel heavy for the rep range listed. Do the circuit 3-5 times, with minimal rest, 3 times per week. On week two, cycle the reps so you're doing 10 lunges/side, 6 presses/side, and 15 rows/side. On week three, 6 lunges, 15 presses, and 10 rows.
By week 4, you'll have your mojo back, guaranteed -- if not sooner.
2. Get re-hooked on the endorphin rush
Everyone who's ever trained regularly knows the sensation of completing a tough workout and feeling like a million bucks. I get giddy---practically manic---after lifting weights. We all know how Arnold described the feeling.
Physical exertion triggers the release of these pleasure hormones, but you don't need to slog through a workout when you're feeling rusty to get it. Embrace the spirit of play you had when you were a kid. Climb a tree. Roller skate. Swim. Hit up a swing-set. Roll down a hill. I'm 100% serious. Remind your body that movement is fun. You'll find yourself not dreading going back to the gym, but actually excited to do it.
This is a joke among my trainer friends, that people just want to eat candy all day---men don't want to work their legs or backs; women don't want to correct their anterior pelvic tilt or lift anything heavier than a can of soup.
But if you're breaking a dry spell, getting fitness back into your routine is more important than that right now. Go to the gym and do those exercises you love. Do them with gusto. Get a taste of the endorphins, have fun for a week or two, then pick up your old program right where you left off.
Taking your fitness seriously can be a double-edged sword; as good as it makes you feel when you're crushing it, it can be seriously demoralizing when you've hit a dry spell.
Here's what I emphasize: the work you've already done is not gone. Your strength is still there. Your ability to express your fitness level is temporarily diminished, but it's no different than sleeping on your side and waking up to a numb arm. Your arm is still there. It just needs more time to wake up.
Moreover, and this is really important, training progress is never linear. Even -- especially -- world-class athletes go through training periods of great productivity, and periods of controlled backsliding. It is the backsliding that makes greater progress possible on the upswing.
Go get started on your upswing. Let me know how it goes.