You're orchid is probably just taking a break.
Many orchids do require a resting period. This is
usually in late autumn or early winter. During this resting period, they may loose their leaves, leaving only the pseudobulbs. That's ok since new growth will come from the pseudobulbs. During this stage, the
plant will need very little watering, only water if the potting soil is completely dried out.
There are 2 orchid pages on this site. You probably read mine.
Barb's (Flower) Orchid page seems to cover what you'll need to know. a link to my page is on the bottom of hers..