This is taken from drweilselfhealing.com :

For times that call for a quick pick-me-up, here’s a yogic
exercise that works faster than a cup of coffee. Commonly known as the bellows breath, I call it the Stimulating Breath.

1.Sit with your back straight and put your tongue in the yogic position, as
described in the box on page 6. Hold it there for the duration of the
exercise.

2.Breathe in and out very rapidly through your nose, keeping your mouth lightly
closed. Your inhalations and exhalations should be of equal length and
as short as possible (as many as three cycles per second, if you can do
that comfortably). You should feel muscular effort at the base of your
neck just above the collarbones and diaphragm (try putting your hands
on these spots to get a sense of movement). The action of your chest
should be rapid and mechanical, like a bellows pumping air.

The first time you try this exercise, keep it up for no longer than 15
seconds, then breathe normally. Each time you do it, increase the
duration by 5 seconds, if you can, until you work up to a full minute.

I recommend practicing every morning when you first get up. This is real
exercise, and you can expect to feel some fatigue in the muscles you
are using at first. At the same time, you should feel a sense of
greater alertness and less mental fatigue, an effect that will increase
with practice.