Feeling dizzy upon waking up is commonly caused by several factors related to bodily changes and conditions during sleep and upon standing. The main reasons include:

• Dehydration : Not drinking enough fluids before bed or overnight fluid loss can cause dehydration, leading to dizziness in the morning.
• Low blood pressure (orthostatic hypotension) : When moving quickly from lying down to standing, blood pressure may drop temporarily reducing blood flow to the brain, causing dizziness.
• Low blood sugar : Low blood sugar levels in the morning, especially if fasting overnight or for people with diabetes, can cause dizziness and shakiness.
• Inner ear issues like Benign Paroxysmal Positional Vertigo (BPPV) : Dislodged crystals in the inner ear can cause spinning sensations or dizziness triggered by head movements, often aggravated in the morning.
• Sleep apnea : Interrupted breathing during sleep can lower oxygen levels and cause dizziness upon waking.
• Medications : Some medications, such as blood pressure drugs, sedatives, antidepressants, and others, can have dizziness as a side effect.

Often, this dizziness is due to the body adjusting from a lying to a standing position or dehydration overnight. If dizziness upon waking is frequent, severe, or accompanied by other symptoms such as fainting, chest pain, or headaches, it is important to consult a healthcare provider for diagnosis and treatment. Maintaining hydration, standing up slowly, managing blood sugar, and reviewing medications may help reduce morning dizziness.