I know this is a narcolepsy forum, but I have had insomnia for about 6 years at diffrent difficulties. For about 4 months now anytime I go to REM sleep(usually second half of the night) I have extreme vivid dreams like I'm in the dream, but never a nightmare and In the morning I will have Inertia for like the first 3 hours. A few times It has lasted all day, but usually just the first 3 hours of the day. If I sleep less or don't go to REM sleep I don't have the morning inertia.
I don't just fall a sleep randomly during the day, but sometimes take a 30 minute nap during the middle of the day. When I nap I never dream drean, but will wake up with like inertia for like 30 minutes. I have no other symptoms that I am aware of.