Feeling nauseous when you wake up can be caused by several factors, including:

• Acid reflux (GERD): Stomach acid can travel up the esophagus during sleep, especially if you lie flat, causing a sour taste and nausea in the morning.
• Low blood sugar: After fasting overnight, blood sugar levels drop, which can cause nausea, weakness, and dizziness.
• Sleep issues: Poor or disrupted sleep affects your body's circadian rhythms and hormones, which can lead to nausea upon waking.
• Dehydration: Not drinking enough fluids overnight can cause mild dehydration, contributing to nausea.
• Anxiety or stress: The gut and brain are connected, and stress or anxiety can manifest as nausea, especially when waking up.
• Diet and hunger: Skipping meals or eating certain foods (especially before bed) can cause morning nausea.

Other possible causes include pregnancy (morning sickness), medication side effects, sinus congestion, and inner ear disturbances. Typically, morning nausea is temporary and not serious but if it persists, it’s good to check with a healthcare provider to rule out underlying conditions like GERD, gastroparesis, or metabolic issues.