Why does my nose get stuffed at night?

Most common reasons are dry air in your room, more nasal congestion if you have rhinitis (either acute or chronic) due to more blood flow and higher venous congestion in supine position and you pay more attention to your body during sleep, i.e. less interaction at night.

Some causes are dust collectors in your bedroom,too dry environment for which a humidifier can help, sleeping too flat which sleeping with head higher than chest would help. Sometimes acid reflux is the cause and head higher than chest in bed can help. You could try taking an antihistamine or use decongestant nasal spray but decongestants can interfere with sleep