How long have you written down your dreams? Did you just start? The decrease could just come from getting over the initial novelty of it. Or your sleep patterns may have changed somewhat, such as having to jump out of bed sooner, not sleeping as long, or just sleeping during different times. Have you experienced any recent changes in your sleep schedule? Regardless, don't sweat it too much, just keep writing down the dreams you do recall.

I haven't yet any success with reality checks, so don't listen to me, but... How about forgetting the mark on your hand and just do an RC everytime you see your hands? I used to do that during a previous incarnation of LD practice. It led to my first LD. Unfortunately, it didn't keep up.