The reasons for tachycardia when sleeping at noon are as follows: 1. If there is a nervous condition or there is something on your mind, you can have tachycardia; 2. If there is tachycardia or other diseases, such as anemia and hyperthyroidism, you can also have tachycardia; 3. If there is cardiac insufficiency or even heart failure, after lying down, it will make the heart load increase due to the increase of the return blood volume, and it will reflexively cause tachycardia; 4. If there is stomach If there is gastroesophageal reflux caused by stomach disease, lying down can also cause tachycardia because of acid reflux into the esophagus and indirectly stimulate the sinus node. It is best to do further examination to see what the cause is, and then do targeted treatment.