If you can feel him move when you lay down, drink cool water or juice, then most likely he's fine.
My second baby did this once in a while. Over all she was a dancer in the womb. Constantly moving throughout the day and night, but once in a while her movement would be slowed dramatically. I would have to lay down and really focus to feel her. Then she would pickup her normal pace in a day or so.
Try not to worry too much, he's probably taking a day off and will get back to his old ways in no time. Or... another possibility is that he has turned around with his back facing your bellybutton. If his kicks and pushes are towards your back you may not be able to feel him as much. My daughter also did this.
The last advice I can give you is this.... If you are truely worried about his lack of movment call the doctor.
Best of luck, and congrats on the little one!!!