Apparently this is a common problem with children between the ages of 2 to 4.  I have been told by my doctor that it is completely normal and sometimes has to do with an independence struggle your child might be having.  In this age range they are continuously exploring the world with a little more independance and while this is a good thing, I have been told, that they also realize that the world has dangers and things they don't understand.  I have been through this twice with my two older daughters my 18mth hasn't started to experience the night terrors yet.  When I was going through this stage, I found that cutting back on the TV they watched helped, as well cutting back on foods near bedtime.  I also tried to reassure them more during the day by giving lots of positive re-enforcement.  Also at this age your child can start to understand more so I would talk to her about things during the day as they came up, and at night I would spend more time in her room right before bed read a story and talk about her day.  I found that it was a chance for me to learn more about how she processed the events we had been through over the course of the day and as I learned more about how she saw things, I was able to know what things she was unsure of what things she might have misunderstood and areas where we needed to boost her confidence .  Just follow your gut feelings and remember that children are sponges and although they seem to be fine with their new found freedom they are also still small and they need your guidence more than ever, it's a big world they just don't understand yet and that can be a little scarey.