One my nostril blows slightly less air than the other is it something dangerous or is it normal because never noticed it before?

Nasal cycle : Asymmetry. If your left nostril becomes congested when on your left side and switches to the right when you turn over, you have exaggerated asymmetry in the automatic nervous system; commonest cause might soound strange but poor diet is often the answer.

Nasal airflow : If you have a new change in nasal airflow that was not there before, and you aren't sick or recently injured in the nose, you may want to see an ENT to check your nose. The normal nasal cycle alternates blood flow from left to right over a 90 min cycle. This frequently causes intermittent, alternating congestion most noticeable when you have a cold or if you have nasal swelling. Hope this helps.