Anna has noticed that for the past three weeks she is unable to sleep for more than five hours at a time,even though she used to regularly get eight hours of sleep per night.She wakes early in the morning and just can't fall back to sleep.What has Anna developed

A)  sleep apnea 
B)  pseudoinsomnia 
C)  somnambulism 
D)  insomnia

Insomnia

A common sleep disorder characterized by trouble falling asleep, staying asleep, or getting restorative sleep, leading to daytime dysfunction and distress.

Unable

Lacking the ability, means, or opportunity to do something.

Sleep

A naturally recurring state of rest for the mind and body, characterized by altered consciousness, relatively inhibited sensory activity, and inhibition of nearly all voluntary muscles.