Most tanners report mood enhancement, relaxation and socialization while soaking up the sun. But tanorexics become very competitive about tanning, and may actually hate their skin and view it as untolerably pale, in the same way anorexics view themselves as hatefully fat even when they're starving. Tanorexics experience the most serious withdrawl symptoms, which include intense anxiety, nausea, and jitters. Since UV light from the sun and tanning beds creates a feeling of euphoria in the brain, it's also likely tanners feel depressed when they are removed from their lights for too long.
Since any tan at all is evidence of sun damage, and tanners continue to ignore medical risks, this has led many dermatologists to push that UV light tanning addiction be recognized as a substance abuse disorder. And just like any substance abuse order, we already have celebrity posterchildren. Wikipedia says "notable figures known to have suffered from tanorexia are Christine Swanson, Jordan Cohen, the British celebrity chef Heston Blumenthal and the cast of the MTV reality show Jersey Shore."