Some soporifics work better than others, depending on the issue and the patient harboring them. Sleep is a multi-stage event if done well, and long enough, and that last one is 'the rub', so-to-speak.

You need roughly 90 minutes to experience the first round of REM sleep where we dream. Interruptions of all kinds, whether anxiety, pain, noises, discomfort due to pillow arrangement or being too warm under too many blankets, etc., will often interrupt each cycle in people with disturbed sleep patterns. When we take a drug that works well for our genotype, it can get us through repeated cycles, and when that happens, we awaken to find ourselves just having dreamed, usually after about 6.5-7.5 hours in total. So, yes, we probably DO dream more, which is good, but we also sleep 'further' and often awaken after one late dream thinking we've been dreaming all night.