Reality testing (or reality checking) is a common method used by people to determine whether or not they are dreaming. It involves performing an action with results that will be different if the tester is dreaming. By practicing these tests during waking life, one may eventually decide to perform such a test while dreaming, which may fail and let the dreamer realize that they are dreaming.

Common reality tests include:

• The nose reality check: Pinch your nose and if you are able to breathe without using your mouth, it is a dream.
• Try to stick your finger through the palm of your hand.
• Looking at one’s digital watch (remembering the time), looking away, and looking back. As with text, the time will probably have changed randomly and radically at the second glance or contain strange letters and characters. (Analog watches do not usually change in dreams, while digital watches have great tendency to do so.)
• Flipping a light switch. Light levels rarely change as a result of the switch flipping in dreams.
• Looking into a mirror; in dreams, reflections from a mirror often appear to be blurred, distorted, incorrect or frightening.
• Looking at the ground beneath one’s feet or at one’s hands. If one does this within a dream the difference in appearance of the ground or one’s hands from the normal waking state is often enough to alert the conscious to the dream state.

Another form of reality testing involves identifying one’s dream signs, clues that one is dreaming. An individual may record their dreams in a Dream Journal and analyse the common themes to determine one’s own Dream Signs. Dream signs are often categorized as follows:

• Action — The dreamer, another dream character, or a thing does something unusual or impossible in waking life, such as being able to fly, being able to walk through walls, being able to change the setting illogically, or noticing photographs in a magazine or newspaper becoming three-dimensional with full movement.
• Powerlessness — There may typically be a sensational loss of bodily strength.
• Context — The place or situation in the dream is strange and includes fictional characters or places.
• Form — The dreamer, another character, or an object changes shape, is oddly formed, or transforms. This may include the presence of unusual clothing or hair, or a third person view of the dreamer.
• Awareness — A peculiar thought, a strong emotion, an unusual sensation, a loss of normal logic, or an altered perception. In some cases when moving one’s head from side to side, one may notice a strange stuttering or ’strobing’ of the image.
• Cohesion — Sometimes the dreamer may seem to teleport to another location in a dream, without a noticeable transition.
• Clocks — Another, unlikely, possibility is that while one looks at a clock or watch, looks away, then looks back, the time would have changed dramatically.

You can find more about the various dream signs in the article Dream Signs in Dreams Interpretation category.