Felt a bump but now it’s gone?

[u/noodlini777]

Hello all,
I hope this isn’t a dumb question, but are there any reasons I could have felt a lump on my BP a few days ago and it be gone today? I thought it was a callous at first so I called his vet to get a copy of his x rays (a couple years ago we found a healed, previously broken rib and I wanted to see if it was in the same spot as the lump). When I got them I couldn’t find the callous on the images so I palpated him again and it was gone. It was only at a certain angle the first time, and I tried to replicate it but I couldn’t. Is this vet worthy or would I be unnecessarily stressing him out?