Hyposomnia literally means "less
(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.