Waking up sweaty, or experiencing night sweats, can have several causes ranging from simple environmental factors to underlying medical conditions. Common reasons include:

• A sleeping environment that is too warm, such as having heavy bedding or a room temperature above the recommended cooler range for sleep.
• Infections that cause fever, making the body sweat to reduce temperature.
• Hormonal imbalances or changes, such as those experienced during menopause, pregnancy, or due to endocrine disorders like hyperthyroidism.
• Low blood sugar (hypoglycemia), especially common in people with diabetes.
• Stress and anxiety which can trigger the body's stress response and increase sweat production.
• Certain medications (antidepressants, steroids, painkillers) and substance use like alcohol or smoking.
• Sleep disorders such as sleep apnea.
• Conditions like hyperhidrosis, which cause excessive sweating without a specific underlying cause.

If night sweats are frequent, severe, soaking sleepwear, or accompanied by other symptoms like fever, weight loss, or pain, it is important to consult with a healthcare provider for diagnosis and treatment.