The findings could pave the way to a better understanding of the causes of insomnia, as well as the development of more personalised treatments for the condition, the researchers say. Thousands of eager people registered on the online platform slaapregister.nl and there answered questions formulated in advance by specialists. Tessa Blanken and and other researchers from the Netherlands Institute for Neuroscience suggest on the basis of the study that there is not one type of insomnia, as previously thought, but five.

Based on the respondents' answers, nearly two thousand of them may suffer from insomnia - they scored high on the survey, but have no confirmed diagnosis. To identify subtypes of the condition, the researchers went beyond examining sleep-related symptoms and also considered other factors, including personality traits, mood, emotions and reaction to stressful situations.

The study authors showed that participants struggling with insomnia could be assigned to one of five categories.

Type 1: People suffering from Type 1 insomnia have high levels of stress. It is associated with vulnerability to negative emotions, including anxiety and worry.

Type 2: There is a moderate level of stress, but the degree of happiness and pleasant experiences is statistically normal.

Type 3: Here there is also a moderate level of stress, but the level of happiness is understated and pleasant experiences are below statistical.

Type 4: Patients tend to have low levels of stress, but have a tendency towards prolonged insomnia in response to a stressful life event.

Type 5: Type 5 insomniacs' stress levels are low and sleep disturbances have not been influenced by stressful life events.

A reassessment five years after the first survey showed that the majority of those surveyed maintained the same subtype.

The categorisation into insomnia types should enable more effective research into the prevention of depression in insomnia patients by focusing on vulnerable individuals. The classification could help prevent this type of illness, the researchers say.

They note that some insomnia practitioners may have concerns about the subtypes because they are largely based on factors that are not directly related to sleep. The authors of the study emphasise that participants in the experiment self-reported and no selection was made as to who should take part. The study group is therefore not necessarily representative of the general population. The researchers also suggest that there may be additional subtypes that have not yet been identified.