Duḥkha is a disturbance of the mind…..

Mind

“Duḥkha is a disturbance of the mind. While sometimes the words sorrow, misery, and disease are used to define duḥkha, it is best identified as a feeling of restriction.
Somehow something deeply disturbs us and we feel restricted.
This restriction is duḥkha…….
We all aim to remove duḥkha……..
That is what Yoga is trying to do.”

TKV Desikachar, Religiousness in Yoga