If you're planning on taking LSD.. don't.

Seriously. Don't even think about it. 

The effects of LSD are not just potentially terrifying, but can even be life-threatening. 

A "bad trip" can consist of intense terror, loss of appetite, sleeplessness, tremor, dry mouth, fear of insanity and death, and much, much more; the experience can vary between users. The effects of LSD are not just potentially terrifying, but can even be life-threatening. LSD users' ability to sense danger can be impaired, meaning they may think they can fly and jump out of a window, or unknowingly walk into the middle of traffic.

"Flashbacks" are a reported phenomenon in which someone who has taken LSD experiences brief LSD induced effects long after taking the substance. These flashbacks are typically triggered by alcohol or marijuana use. Although there are reported cases of flashbacks, it is widely debated over whether it is a legitimate phenomenon. After all, over 70% of LSD users claimed to have never experienced flashbacks. 

Although flashbacks are not considered a medical condition, there is something called Hallucinogen Persisting Perception Disorder which is. This syndrome, unlike flashbacks, involves long, persistent LSD-like visual changes. It is suggested that HPPD is rare, but this is not taking into consideration the number of potential LSD users who may have these symptoms but are reluctant to share the knowledge of their past drug use with their health care practitioner. Like all things psychological (this is an exaggeration), there is no clear cut answer for the cause of HPPD. A study of HPPD subjects showed no abnormalities in their EEGs. The explanation that LSD lingers in the body long after ingestion have been proved false. Some believe that HPPD is a type of post-traumatic stress disorder brought on by a reminder of the original LSD trip.