Really bad startle reflux?

My baby is five almost six weeks and has been startling really bad when on her back. Typically when changing diapers or letting her sit in the boppy.

She will startle, just hold it, stop breathing for a moment, and then start screaming. We will hold her to calm her, but it seems really bad. Then today, she got it worse then before. She startled, held it for a long time, stopped breathing, and turned red in the face. I picked her up to calm her and she held it even then. It took her a moment to start screaming and then I held her till she calmed down. Just seems like it’s getting worse! Anyone have this with their babies?

Swaddling helps, but she isn’t swaddled all the time.