Some philosophers, such as Jeremy Bentham, Baruch Spinoza, and Descartes, have hypothesized that the feelings of pain (or suffering) and<unk>  are part of a continuum. There is strong evidence of biological connections between the neurochemical pathways used for the perception of both<unk> , as well as other psychological rewards.
Pain and pleasure
Pain out of proportion
Meditation and pain
Wellness 
Pain tolerance
Baricity
Comfort
Drug liking