I think what happened was I put it down on a chair while I photographed a tomb in St Mary's, Bury St Edmunds. I had a guide book in my hand too- only just purchased- and that has gone as well.
Oddly enough a couple of minutes after walking away from the tomb I found a flat cap on the floor at the other end of the church. I think this must have been the universe giving me a nudge- as if to say "Have you forgotten anything?" But, like a good citizen, I handed the cap to the lady at the door and failed to take the hint.
Today, in Hastings, I bought myself a replacement.
This is the photograph I was taking.

The tomb belongs to John Baret, who died in 1467. It's one of those cadaver jobbies that were so popular at the time. Unusually it dispenses with the clothed effigy. Baret was rich- but presumably not that rich. He had it made before he died. Perhaps he kept it in his bedroom- as John Donne reportedly did with the effigy of himself in his shroud.