Pain by it’s essential nature is a psychological event, meaning that is is perceived by (in) the mind and is therefore subjective and cannot be measured directly. 

Pain is defined as a negative sensory event, usually associated with a threat to life or limb. It is usually accompanied by suffering, which is the emotional response to pain (even non-physical). For example, anxiety is an emotional pain that is accompanied by the emotion of suffering.

Pain and suffering do not always occur in sync, as the pain of childbirth usually has positive emotions that override the negative, and the insignificant damage of being bopped by a sibling or being disrespected by a partner can cause much suffering.