NeilMed sinus rinse feels awful- any tips?

I've never liked nasal rinses, but I know they're critical, so I just tried my first 36 hours post-op. It was terrible. No matter how far I leaned forward or how gently I went, it just kept coming out of my mouth. I'm in tears, I want to throw up, and everything stings. Twenty minutes later I'm still holding ice packs to my face and getting a headache. I don't know how I'm going to do this twice a day. Does anyone have tips? Do I have to do half the bottle in one nostril at a time, or can I go back and forth between nostrils? Should I wait until I'm at peak Sudafed? Are there other brands that are gentler?