Sleep and Medical/Psychiatric Comorbidity
Bidirectional relationships
Sleep and medical/psychiatric illness interact in both directions. Depression is strongly associated with insomnia and with REM abnormalities (short REM latency, increased REM density); insomnia is a risk factor for incident depression and an independent treatment target. Obstructive sleep apnea increases risk of hypertension, atrial fibrillation, stroke, and insulin resistance; it is common in heart failure and in patients with resistant hypertension. Chronic insomnia and short sleep associate with cardiometabolic risk.
Disease-specific considerations
In COPD, nocturnal hypoxemia and overlap syndrome (COPD plus OSA) worsen outcomes; supplemental oxygen alone can blunt hypoxic drive and worsen hypercapnia. In heart failure, both OSA and central sleep apnea (Cheyne-Stokes) occur; treatment targets the underlying cardiac disease. In epilepsy, sleep deprivation lowers seizure threshold, and some antiseizure medications alter sleep architecture. In chronic pain and fibromyalgia, nonrestorative sleep is prominent. In psychiatric illness, sedating medications can worsen apnea and weight; REM-suppressing drugs can confound MSLT interpretation.
Assessment and treatment
Screen for sleep disorders in patients with cardiometabolic and psychiatric disease. Treat the primary condition and the sleep disorder concurrently; CBT-I is effective in comorbid insomnia and does not require waiting for depression remission. Be cautious with benzodiazepines and opioids in patients with sleep-disordered breathing.
Traps
Questions test directionality (does apnea cause hypertension, or the reverse?), drug effects on sleep architecture, and the risk of sedating agents in respiratory disease. Do not assume treating apnea alone resolves depression or insomnia.
Rule of thumb
Treat both conditions in parallel; in comorbid insomnia, CBT-I works even while the medical or psychiatric condition is active.