You may have encountered a random failure of some part you did not replace in the last 4 years, you did real well for a Predicta.
Anyone could assume the worst-case: flyback arc-short is possible as I have witnessed color sets behave this way prior to losing HV for good, which yours didn't, fortunately! But shorted turns (AKA internal spot-welds between adjacent windings) never fix themselves.
Your HV came back because whatever part was failing decided to heal itself on a cold start. Get some freeze spray after all the parts around the horizontal oscillator. I am assuming H - jitters caused by H-hold or H-range pots being dirty or having tin-whiskers. I hope its that simple for you.
There are some Predicta-savvy techs here, but I avoid
THOSE Philco products myself.
Most all us Philco-techs would agree: OEM Philco caps/resistors/pots are all
SUSpect until confirmed otherwise
!