One thing humans do seem to be evolutionarily adapted to is pushing ourselves into altered mental states using a combination of hunger, dehydration, lack of sleep, rhythmic music, meditation, gradual hyperventilation, and the consumption of hallucinogenic plants. The associated practices (tribal rituals, spirit quests, ecstatic prayer, etc.) are fundamental to many early human cultures, and it was expected that everyone would participate in them. I would hazard to guess that sleeping while in such altered states would make lucid dreaming "easier"; a lucid dream—one that you've slipped into without realizing you had fallen asleep—fits the description of the ideal outcomes of many rituals more closely than, say, hallucinations or absent seizures do.