[weed]
That is extremely interesting about the sleep part, I asked the question as a good friend has early stages of dementia at a young age, they have given up getting stoned hoping it will help, but like you have irregular sleep, waking up after just 4 hours sleep plus having vivid dreams or nightmares.
Perhaps having a smoke or cookie in the evening might help them sleep better.
weed does change REM sleep, it delays its onset and there is less of it. having a proper balance of REM vs other cycles is important to cognitive abilities and such.
so if that person has sleep issues related to timing and frequency of dreams it may help.