Nonetheless, the value of distinguishing this type of insomnia from other types is debatable due to the relatively low frequency of SSM being reported.Sleep state misperception can also be further broken down into several types, by patients who:

report short sleep (subjective insomnia complaint without objective findings)or no sleep at all (subjective total insomnia)
report excessive daytime sleepiness (subjective sleepiness complaint without objective findings)
report sleeping too much (subjective hypersomnia without objective findings)

Validity
The validity and reliability of the sleep state misperception as a pertinent medical entity was questioned. A study found poor empirical support for this diagnostic item. Symptoms and diagnosis
This sleep disorder frequently applies when patients report not feeling tired despite their subjective perception of not having slept. Generally, they may describe experiencing several years of no sleep, short sleep, or non-restorative sleep. Otherwise, patients appear healthy, both psychiatrically and medically. (That this condition is often asymptomatic could explain why it is relatively unreported.) However, upon clinical observation, it is found that patients may severely overestimate the time they took to fall asleep—often reporting having slept half the amount of time indicated by polysomnogram or electroencephalography (EEG), which may record normal sleep. Observing such discrepancy between subjective and objective reports, clinicians may conclude that the perception of poor sleep is primarily illusionary. Alternatively, some people may report excessive daytime sleepiness or chronic disabling sleepiness, while no sleep disorder has been found to exist.
Furthermore, rumination and poor coping resources may play a significant role in sleep misperception. Spectral analysis
According to a May 2014 article published in New Scientist, spectral analysis may help clinicians find objective evidence for sleep state misperception:

[...] it uncovered [...] subtle differences in the EEGs of sleeping insomniacs: alpha waves – signatures of wakefulness that are supposed to show up only in early sleep – were intruding into deep sleep. [...] [psychologist and sleep researcher Michael] Perlis. But Andrew Krystal of Duke University in Durham, North Carolina, used spectral analysis to quantify just how much they were intruding. Krystals non-sleepers not only had a greater proportion of these alpha disturbances, but the alpha waves were bigger and the delta waves were correspondingly smaller. That wasnt all. When Perlis and other researchers applied spectral analysis algorithms to the EEGs of their sleeping insomniacs, they found different patterns, fast waves known as beta and gamma (Sleep, vol 24, p 110). Normally, these are indicators of consciousness, alertness and even anxiety [...] Like alpha waves, Perlis calls these beta and gamma waves "intrusions" into normal sleep: "Its as if somebody is playing with the switch – boop, boop – flipping at a mad rate between wake and sleep". Distinction from insomnia
What is considered objective insomnia, unlike SSM, can easily be confirmed empirically through clinical testing, such as by polysomnogram. Those who experience SSM may believe that they have not slept for extended periods of time, when they in fact do sleep but without perceiving it.