preparation and only a moment for ignition.

Through the dream-work the dream process now gains either sufficient
intensity to attract consciousness to itself and arouse the
foreconscious, which is quite independent of the time or profundity of
sleep, or, its intensity being insufficient it must wait until it meets
the attention which is set in motion immediately before awakening. Most
dreams seem to operate with relatively slight psychic intensities, for
they wait for the awakening. This, however, explains the fact that we
regularly perceive something dreamt on being suddenly aroused from a
sound sleep. Here, as well as in spontaneous awakening, the first glance
strikes the perception content created by the dream-work, while the next
strikes the one produced from without.

But of greater theoretical interest are those dreams which are capable
of waking us in the midst of sleep. We must bear in mind the expediency
elsewhere universally demonstrated, and ask ourselves why the dream or
the unconscious wish has the power to disturb sleep, _i.e._ the
fulfillment of the foreconscious wish. This is probably due to certain
relations of energy into which we have no insight. If we possessed such
insight we should probably find that the freedom given to the dream and
the expenditure of a certain amount of detached attention represent for
the dream an economy in energy, keeping in view the fact that the
unconscious must be held in check at night just as during the day. We
know from experience that the dream, even if it interrupts sleep,
repeatedly during the same night, still remains compatible with sleep.
We wake up for an instant, and immediately resume our sleep. It is like
driving off a fly during sleep, we awake _ad hoc_, and when we resume
our sleep we have removed the disturbance. As demonstrated by familiar
examples from the sleep of wet nurses, &c., the fulfillment of the wish