Thank you for asking such a fascinating question. You are indeed a keen observer. There are many blood vessels in the soft tissues of the nose. Called turbinates, these blood vessels can swell. Swollen tisuues in the nose can block the nasal passages, creating congestion.
During sexual arousal, the sympathetic nervous system kicks in and the blood vessels constrict. There is less blood flow to the nose and the nose opens up. A potential side effect of this is that one may then develop a runny nose. This has bene reported to happen during sexual activity or afterwards.
There is less congestion for 45 to 60 minutes. After orgasm, the parasympathetic nervous system takes over. The nose will start to slowly return to normal.
The turbinates of the nose contain erectile tissue, and nasal stuffiness during sexual activity is a well known phenomenon (honeymoon rhinitis).
