I will write on hallucinogen abuse and intoxication later.

Hallucinogen Persisting Perception Disorder is the fancy DSM-IV name given for flashbacks caused by LSD and other hallucinogens.  These are brief but uncomfortable visual and other disturbances that continue to occur even years after the drug abuse has stopped.  The disturbances may include geometric forms, peripheral-field images, flashes of color, intensified colors, trailing images, perceptions of entire objects, afterimages, halos around objects, of things appearing too large or too small.  They may be more likely to occur in dark environments or to be brought on by various drugs, anxiety or fatigue, etc.  I remember one former LSD user would hallucinate Smoky the Bear along the roadside while riding in cars at night.  While it sounds funny, she found it an unpleasant experience. 

Case Report of Treatment with Reboxetine: In an Israeli report, a patient who did not improve when given two different SSRI trials did improve after being switched to reboxetine 6 mg/d with a 6 month follow-up. LSD-induced Hallucinogen Persisting Perception Disorder with depressive features treated with reboxetine: case report. Lerner AG, Shufman E, Kodesh A, Kretzmer G, Sigal M. Isr J Psychiatry Relat Sci. 2002;39(2):100-3