Hypoxia symptoms vary depending on the severity, underlying cause and what parts of your body are affected. When your oxygen is low, you might feel like you can’t breathe or think properly. Some hypoxia symptoms include: Restlessness. Headache. Confusion. Anxiety. Rapid heart rate (tachycardia). Rapid breathing (tachypnea). Difficulty breathing or shortness of breath (dyspnea). Severe hypoxia can cause additional symptoms: Slow heart rate (bradycardia). Extreme restlessness. Bluish skin (cyanosis).