We have spoken in an earlier chapter of the trouble sometimes
experienced in inducing a nervous child to go to sleep. In older
children insomnia is common enough. Even when sleep comes it may be
light and broken, as though the child slept just below the surface of
consciousness and did not descend into the depths of sound and
tranquil slumber. We have often noticed how different is the estimate
of the patient from that of the nurse as to the number of hours of
sleep during the night. The sick man maintains that he has hardly
slept at all, whilst the nurse, drawing us aside, whispers in our ear
that he has slept most of the night. In estimating sleep we have to
consider not only its duration, but also its depth, and the patient
who denies that he has slept at all has lain perhaps half the night
with an active restless brain betwixt sleep and wakefulness. Often
enough when he comes to consider in the morning the problems that
vexed his soul at midnight, he is quite unable to recall their nature,
and recognises them as the airy stuff that dreams are made of.
Although in a sense asleep he may have retained a half-consciousness
of his surroundings and a sense of despair at the continued absence of
a sounder sleep.

With nervous children we are apt to find sleep which is of little
depth and which constantly shows evidence of a too-active brain. The
body is tossed to and fro, words are muttered, and the respiration is
hurried and with a change in rhythm, because there is no depth of
anæsthesia. The body still responds to the impulses of the too-active
brain. From the nature of his dream--as shown by chance words
overheard--we may sometimes gather hints to help us to find where the
elements of unrest in his daily life lie. Sleep-walking is only a
further stage in this same disorder of sleep, in which the dream has
become so vivid that it is translated into motor action.