How old is your plant? Is it in the ground or in a pot? Where do you live? How much sun does it get? How long have you had it?

The questions daveh asked are the ones I would ask you, but I would also ask how much water it gets, how your drainage is, and if it gets any nitrogen if you have it in a pot. My parritae is now 4 years old and this time of year it is dropping a fair number of old leaves, but it is also putting on a lot of new growth and branching at nearly every new node right now.

If it's a new plant in a new location, you should expect it to go through a period of adjustment, possibly with some leaf loss and slowed growth. A picture of some sort would help a lot so people can figure out whether the problem is "normal" or something to worry about.

Do you have other Tacsonias? How are they doing under your conditions?