Why do I feel tears welled up in my eyes during irrigation

Normally, tears travel to the nasal cavity through a really narrow tube (naso-lacrimal duct); and tears welled up when the tube is blocked. Therefore, when the tube is partially obstructed due to rhinitis or stuffed nose, the additional pressure given by the irrigation would block the tube and cause the tears to well up. At this stage, irrigation can still be continued with a lower water pressure; however, if tear does come out continuously, then stop the irrigation and retry after 3 ~ 4 hours. If this issue occurs every time you use the irrigation, then we suggest you to consult your doctor to check if there is any abnormality of the sphincter inside naso-lacrimal duct.