Hi, I am a new ish owner of a 74 superglide. I changed the oil in preparation of my first long journey which went great. However I took it for a ride today (Boxing Day) and half way through my ride I noticed I had almost zero engine pressure and at idle it was zero but when reved it just got out of the yellow zone.

Before i Ieft and when just started up there was plenty of pressure..

Should I be worried? And how do I fix it?