our sleep becomes imperfect; and when that desire or aversion is so strong,
as to produce voluntary motions, we begin to awake; the larger muscles of
the body are brought into action to remove that irritation or sensation,
which a continued posture has caused; we stretch our limbs, and yawn, and
our sleep is thus broken by the accumulation of voluntary power.

Sometimes it happens, that the act of waking is suddenly produced, and this
soon after the commencement of sleep; which is occasioned by some sensation
so disagreeable, as instantaneously to excite the power of volition; and a
temporary action of all the voluntary motions suddenly succeeds, and we
start awake. This is sometimes accompanied with loud noise in the ears, and
with some degree of fear; and when it is in great excess, so as to produce
continued convulsive motions of those muscles, which are generally
subservient to volition, it becomes epilepsy: the fits of which in some
patients generally commence during sleep. This differs from the night-mare
described in No. 3. of this Section, because in that the disagreeable
sensation is not so great as to excite the power of volition into action;
for as soon as that happens, the disease ceases.

Another circumstance, which sometimes awakes people soon after the
commencement of their sleep, is where the voluntary power is already so
great in quantity as almost to prevent them from falling asleep, and then a
little accumulation of it soon again awakens them; this happens in cases of
insanity, or where the mind has been lately much agitated by fear or anger.
There is another circumstance in which sleep is likewise of short duration,
which arises from great debility, as after great over-fatigue, and in some
fevers, where the strength of the patient is greatly diminished, as in
these cases the pulse intermits or flutters, and the respiration is
previously affected, it seems to originate from the want of some voluntary
efforts to facilitate respiration, as when we are awake. And is further