unclear, senile, stupid, joke
恍 centers on a mental state that is hazy or not sharp: being unclear, senile, or stupid. The joke sense is a natural extension of acting foolish or out of touch.
恍 combines 忄 (heart/mind) with 光 (light), suggesting a mind that is bright but unfocused or scattered, leading to unclear thinking.
The heart/mind radical 忄 beside 光 (light) suggests a mind flooded with light so that thoughts become hazy and unclear, like a senile person or someone making a silly joke.
For コウ, imagine an unclear, senile joke that makes you say 'koh' in confusion: koh -> コウ, and the hazy mind produces a stupid joke.