1Cold water on your face, especially around the eyes and cheeks, slows things down fast. Splash it, or hold a cold flannel there for half a minute.
This is one of the few things that works when you are too far gone to concentrate on anything. It asks for no skill and no privacy beyond a tap. Lean over the sink, hold the cold against your face, breathe out slowly while it is there. If cold makes you flinch or feels punishing, leave it and use something warmer instead.
Islamic evidence
and sent down water from the sky to cleanse you (Quran 8:11). The same verse ends with hearts made strong and feet made firm, which is close to what you are reaching for at the sink.
“Remember when He gave you sleep as a reassurance from Him, and sent down water from the sky to cleanse you, to remove Satan’s pollution from you, to make your hearts strong and your feet firm”
Qur'an 8:11
Psychological evidence
There is no trial of face cooling in this evidence set, so treat the mechanism as a plausible one rather than a proven route. The nearest relevant study randomised people to hear relaxing music before a laboratory stressor and found their autonomic nervous system recovered faster, while the effect on cortisol was less clear. That much supports the general idea that a simple outside input can shift the body's state, without telling you how much cold water does.
Thoma MV, La Marca R, Brönnimann R, Finkel L, Ehlert U, Nater UM. (2013). PloS one · doi
Review detail
Why it works. Cold on the face triggers a reflex that slows the heart, and it does that without needing your cooperation.
When not to. Skip the cold if you have a heart condition, unless a doctor has told you it is fine.