atrophy, go numb, be paralysed
痿 centers on a loss of function or strength in the body: muscles wasting away (atrophy), limbs going numb, or becoming paralyzed.
痿 combines 疒 (sickness) with 委, which likely contributes the sound and may suggest a bending or weakening idea. The exact historical development is uncertain.
The sickness enclosure 疒 wraps around 委, like a body bent and weakened by illness. Picture muscles wasting away until the limbs go numb and paralyzed.
For イ, imagine an eagle (イーグル) with atrophied wings, unable to fly: eagle -> イ, and the sickness enclosure shows its weakened state.