Great Master Yunmen said,
“When the light does not penetrate freely, there are two kinds of sickness. One is when all places are not clear and there is something before you. Having penetrated the emptiness of all things, subtly it seems like there is something—this too is the light not penetrating freely.
Also, the dharmakaya has two kinds of sickness—one is when you manage to reach the dharmakaya, but because your clinging to Dharma is not forgotten, your sense of self still remains, and you fall into the realm of the dharmakaya.
Even if you can pass through, if you let go, that won’t do. Examining carefully, (to think) ‘What breath is there?’—this too is sickness.”
-Book of Serenity, Case 11 & from the Record of “Gate of the Clouds”