Reiki and Vipassana both are quite popular practices worldwide. Vipassana has the core purpose of observing subtle sensations in one’s body while remaining at equanimity, hence clearing both good and bad sanskaras (conditioning of mind) we have, making our chitta (mind) cleaner and cleaner to achieve the ultimate state of no backlog of sanskaras.
If one observes the breathing, it is very easy to find out which nostril is active. Daily, around sunrise, alternatively each nostril gets active for around 1 hour. Hence, in a day, each nostril is active for around 12 hours in alternate pattern.