Being a slang for "having eaten too much bread in one sitting", "painful" is derived from the French word "pain" (meaning "bread") and the English suffix "-ful".
After binge-eatingtoo much bread in one sitting, I'm now feeling painful due to having my stomach full.
While our lifespan is the number of years we will live, our healthspan is the number of healthy years we will have and our sexspan is is the number of years we will continue to be healthy enough to continue having an active sex life.