These four are distortions of perception, thought & view:
• Sensing no change in the changing,
• Sensing pleasure in suffering,
• Assuming "self" where there's no self,
• Sensing the un-lovely as lovely.
Delusion is a mental illness that causes all sorts of suffering; mental health can be restored by correcting the flaws in how the mind operates.
"Vipallasa Sutta: Distortions of the Mind" (AN 4.49), translated from the Pali by Andrew Olendzki. Access to Insight (Legacy Edition), 2 November 2013, http://www.accesstoinsight.org/tipitaka/an/an04/an04.049.olen.html .