Which of the following is an indication of a potential overdose from hallucinogens?

Feeling disconnected from one's body or experiencing a sensation of "floating" is a known indication of hallucinogen use, particularly at higher doses, which can result in a loss of reality and a profound shift in perception. Hallucinogens, such as LSD, psilocybin, or mescaline, can cause extensive sensory alterations and dissociation, where individuals may feel detached from their thoughts or surroundings. This symptom is tied to the drug's psychoactive effects, which can lead to confusion and anxiety in some cases.

In contrast, the other choices indicate different physiological or psychological responses that do not specifically highlight overdose scenarios associated with hallucinogens. Increased heart rate can occur with various forms of drug use and is not exclusive to overdose situations. Improved focus and clarity are generally not effects of hallucinogens, as they often produce mental confusion. Sudden calmness, while sometimes a potential response to certain substances, does not correlate with hallucinogen overdose and is thus not an appropriate indication of an adverse reaction.