The main purpose of this study is to understand how insomnia (compared to good sleep) may affect the response of the body to a repeated physiological challenge, such as inserting the hand in ice-cold water for several times in a row. In particular, the investigators are interested in the response of markers that can be associated with stress, such as blood pressure and stress hormones.

Sleep is critical for the regulation and maintenance of biological systems, and sleep deficiency, such as insomnia, has been shown to be associated with elevated risks for cardiovascular, metabolic, and mood disorders.

Despite the high prevalence of insomnia in the population, the investigators understanding of the biological consequences of the disorder with respect to inflammatory, autonomic, and stress system markers is limited, and often not consistent.

In addition, insomnia may not only alter the basal activity of these systems, but may change their reactivity to other stressors and challenges. In support of this assumption are findings showing that poor sleep quality in healthy individuals is associated with a stronger biological response to a stressful challenge, such as the cold pressor test. This test involves the immersion of the hand in ice-cold water. It is one of the most commonly used laboratory physiological challenge tests, provoking not only unpleasantness, but also increases in stress and inflammatory markers.

Investigations of such system's reactivity to challenge may elucidate systems abnormalities that the investigators do not capture by only assessing basal system's levels. For example, in patients with rheumatoid arthritis, basal inflammatory levels are normal, but the response to a physiological stress challenge (cold pressor test) is amplified.

To the investigators knowledge, no studies have measured how insomnia may affect the reactivity of biological systems to a stressful challenge, which may serve as an important indicator of system's dysregulation and associated disease risk.

In this light, the primary goal of this proposal will investigate whether stress-related systems are more reactive to a physiological stressful challenge in insomnia disorder compared to healthy controls.

Inclusion Criteria:

• Women and men between the ages 18-55 years
• Blood chemistry in the normal range
• BMI less than or equal to 35

Specific to insomnia group:

• Diagnosis of insomnia disorder based on DSM-V criteria

Specific for control group:

• Good quality and quantity sleep

Exclusion Criteria:

• Active infection/disease.
• History of neurological, chronic pain, immune, cardiovascular, liver/kidney, or metabolic disorder
• History of psychiatric disorders within the last 6 months prior to study start
• Sleep disorders other than insomnia
• Reynaud's disease
• Psychotropic, sleep, or any other medications or herbs interfering with the inflammatory, autonomic, or HPA system in the last 2 weeks prior to study start, except oral contraceptives
• In psychotherapy or any other behavioral interventions at study start
• Donation of blood or platelets within 3 months of hospital visits
• Pregnant/nursing.
• Substance abuse.

• Individuals suffering from insomnia disorder
• Healthy control sleepers

Adverse event data were collected over a 9-hour period for each particpant.