Sleepy meditations

I  have a difficult time staying awake when I meditate!  Location, time of day, physical position do not seem to impact this.  After I am able to stop thinking, I am aware of a short time of silence, then I vision (or is it dreaming), then I start to nod off.  I feel a strong desire to nap.  Sometimes I indulge this desire, sometimes I force myself into wakefulness.  I enjoy sleeping, going to bed around 10, falling asleep right away, awaking once or twice during the night but falling right back into sleep, and awaking between 5 and 6 each morning.  I’m generally alert and not tired during the day.  Any insights or recommendations?