Cognitive euphoria (semantically the opposite of cognitive dysphoria) is medically recognized as a cognitive and emotional state in which a person experiences intense feelings of well-being, elation, happiness, excitement, and joy.  Although euphoria is an effect (i.e. a substance is euphorigenic),   the term is also used colloquially to define a state of transcendent happiness combined with an intense sense of contentment.  However, recent psychological research suggests euphoria can largely contribute to but should not be equated with happiness. 
Cognitive euphoria is often accompanied by other coinciding effects such as physical euphoria and tactile enhancement. It is most commonly induced under the influence of moderate dosages of opioids, entactogens, stimulants, and GABAergic depressants. However, it can also occur to a lesser extent under the influence of hallucinogenic compounds such as psychedelics, dissociatives, and cannabinoids.
- American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.), 826. Arlington, VA: American Psychiatric Publishing. | https://doi.org/10.1176%2Fappi.books.9780890425596.GlossaryofTechnicalTerms
- Drevets, W. C., Gautier, C., Price, J. C., Kupfer, D. J., Kinahan, P. E., Grace, A. A., ... & Mathis, C. A. (2001). Amphetamine-induced dopamine release in human ventral striatum correlates with euphoria. Biological psychiatry, 49(2), 81-96. | https://doi.org/10.1016%2FS0006-3223%2800%2901038-6
- Jônsson, L. E., Änggård, E., & Gunne, L. M. (1971). Blockade of intravenous amphetamine euphoria in man. Clinical Pharmacology & Therapeutics, 12(6), 889-896. | https://doi.org/10.1002%2Fcpt1971126889
- Synofzik, M., Schlaepfer, T. E., & Fins, J. J. (2012). How happy is too happy? Euphoria, neuroethics, and deep brain stimulation of the nucleus accumbens. AJOB Neuroscience, 3(1), 30-36. | https://doi.org/10.1080%2F21507740.2011.635633
- Lucas, R. E., Diener, E., & Suh, E. (1996). Discriminant validity of well-being measures. Journal of personality and social psychology, 71(3), 616. | https://doi.org/10.1037%2F0022-35220.127.116.116