Hyposomnia literally means "
less(hypo)
sleep(somnia)". Hyposomniacs do not lack sleep, they simply do not need as much sleep as a
normal individual. Specifically, they sleep less than 6 hours per night, but are adequately rested. Side note: According to
studies* this is particularly common amoung the
elderly, although so is
insomnia.
The difference between hyposomnia and insomnia is that hyposomniacs do not need as much sleep, whereas insomniacs need more sleep, but do not get it.
*I do not have the references to those studies right now, but if I remember and can find my Psych notes, I'll add them.