Opiates make me feel weird when I am awake, so I actually prefer to take them before I go to bed (if I take them at all - they really don’t do a very good job of relieving pain for me - usually ibuprofen and a muscle relaxant works better). The weirdest dreams I’ve ever had have been when I’ve had a fever - the minute my head hits the pillow I start in with the bizarre stuff - I barely need to be asleep.
I still remember a dream I had years ago where I was the foreman in a baby-making factory - we literally made babies on an assembly line, and as they sat on the conveyor belt they’d get bigger and smaller like Alice through the looking glass. That dream made me afraid of my own brain.