Noun
A sudden feeling of dizziness and/or euphoria, such as:
orthostatic hypotension, due to low blood pressure, for example when standing up suddenly.
nicotine rush, for example in people who seldom smoke, or when smoking on an empty stomach.
a rush induced by mind-altering drugs.
a rush due to emotional agitation or excitement, for example when seeing someone one is in love with.
(figuratively) Something exciting or thrilling.
Source: en.wiktionary.org