Hypercapnia occurs when you have too much carbon dioxide in your bloodstream. It usually happens as a result of hypoventilation, or not being able to breathe properly to get oxygen into your lungs.
Symptoms of hypercapnia include flushed skin, drowsiness or inability to focus, mild headaches, feeling disoriented or dizzy, shortness of breath, and being abnormally tired or exhausted. More severe symptoms of hypercapnia include unexplained feelings of confusion, abnormal feelings of paranoia or depression, abnormal muscle twitching, irregular heartbeat, hyperventilation, seizures, panic attack, and passing out.
Tim Jewell, Hypercapnia: What Is It and How Is It Treated?, Health Line (updated May 2, 2017), https://www.healthline.com/health/hypercapnia#outlook.