If lucid means "clear and easy to understand," then its opposites could be:
* Confused
* Obscure
* Vague
* Ambiguous
* Unclear
* Muddy
* Opaque
If lucid means "mentally clear and alert," then its opposites could be:
* Confused
* Delirious
* Disoriented
* Unconscious
* 昏迷 (hūn mí) - coma (Chinese)
* Incoherent
If lucid means "vivid and realistic," then its opposites could be:
* Dreamlike
* Fantastical
* Unreal
* Hallucinatory
The best opposite word will depend on the specific situation in which you are using "lucid."