Lying down on your back or on your side can make a difference when you have a runny nose due to the effects of gravity and the position of your nasal passages:
1. **Gravity**: When you lie down on your back, gravity helps drain mucus from your nasal passages and sinuses, allowing it to flow more easily out of your nose. This can provide temporary relief from congestion and help alleviate a runny nose.
2. **Nasal Passage Position**: When you lie on your side, one nostril may become more congested than the other, depending on which side you're lying on. This can temporarily reduce the flow of mucus from the congested nostril, providing some relief from a runny nose.
However, it's important to note that lying down may not completely alleviate a runny nose, especially if it's caused by factors such as allergies, colds, or sinus infections. In addition to changing your sleeping position, other remedies such as using saline nasal sprays, staying hydrated, using humidifiers, and taking over-the-counter medications may also help relieve symptoms and promote nasal drainage. If your runny nose persists or worsens, consult a healthcare professional for further evaluation and treatment.