Inspiration is a tricky little bugger. It plays hide and seek, arrives when you least expect it, and leaves without a trace.....sometimes for weeks at a time. If you think your job as an artist is just to paint, draw, and create then boy are you in for a surprise.
Many artists feel alone when they're uninspired. They wonder if others go through the same thing (yes we do) and wonder if other artist's slumps have lasted as long as their own (yes they have). But please take comfort in this fact: losing and gaining inspiration is part of being an artist. It is the ebb and flow of creativity; a natural swing of things that you will continually try to weather and work with.
It's careful balance. Don't push too hard when you're just not inspired, but also take responsibility and try to gain that inspiration back. Reading books about your favorite artists, visiting museums, going for a long walk on a beautiful day, whatever works for you. Sometimes the best thing to do is take a break from drawing and do something completely different for a while. That way you'll return to your desk feeling refreshed (of course don't do that sort of thing when you're on a tight deadline!).
The main point is this: don't let it get you down or scare you. It's just the wave pulling back from the sand for a bit. It always comes back. Believe me, I have to remind myself of that many many times.