These guys make some good points. Remember, it could simply be a recall dry spell. Dry spells are often caused by some of the things mentioned above, but it can be difficult to pinpoint sometimes. Just stay confident and remain positive. Fall asleep knowing, 100% in your mind, that you will dream and remember the dream. You could always set some alarms throughout the night and wake up right after (or toward the end of) your REM periods. The dream will be fresh in your mind. I'd recommend setting alarms for after 4 hours of sleep, then 2 hours later, then 1 hour increments for the rest of your sleep period. Wake up, write down your dream, set next alarm, then return to sleep. A few nights of this can help you jump start that recall again. Good luck to you!