Final answer:
MDMA, also known as ecstasy or molly, is a euphoriant and hallucinogen that causes euphoria and sensations of flying, social withdrawal, and nystagmus.
Step-by-step explanation:
The drug that causes euphoria, feelings like "flying above the dance floor," social withdrawal, and nystagmus is MDMA (3,4-methylenedioxymethamphetamine), commonly known as ecstasy or molly. This stimulant and hallucinogen is a member of the amphetamine class and acts as a euphoriant and empathogen, often taken in tablet form. MDMA is characterized by its ability to produce intense feelings of pleasure, emotional warmth, and increased energy, while also enhancing serotonergic transmission significantly more than classical stimulants like amphetamine. High doses of MDMA can lead to brain toxicity and even death. It is important to note that MDMA is a Schedule I controlled substance, with significant potential for abuse and no accepted medical uses in treatment as of the time of this response.