The condition may be distressing and painful for the patient. More positive thoughts can encourage more creative responses to difficult problems or distressing situations. Shortness of breath is a common symptom and is often the most distressing. In some circumstances (particularly families and relationships) this might be emotionally distressing. Only if it was distressing would homosexuality be classified as a mental illness. Inability to effectively perform these tasks can be particularly distressing to patients. In addition, chronic thought disorder is typically distressing. Fantasies accompany "intrusive thoughts about killing someone that are associated with other distressing psychopathological processes". The division of distressing dreams within REM sleep is subtle. The experiment involved participants watching emotionally distressing video footage. Darwin found lectures dull and surgery distressing, so he neglected his studies. Not all who experience hallucinations find them to be distressing. Sadness is also distressing, yet is widely believed to be an evolved adaptation. Junior undergoes chemo and suffers distressing side effects. Although the removal is often painless, this can be distressing for the patient, especially children.