Sudden change in time keeping question

[jb335]

I have a 16750 8.4 serial (1984) that I acquired a couple months ago with unknown service history. I only have a two watch collection so I split wearing them pretty much every other day so they stay wound. The 16750 has been keeping AMAZING time in the two months I've had it with consistently only gaining 1 second a day. Unbelievably good.

Well, I just got back from a ten day vacation out of the country where I did not bring my 16750. I just left it home so it sat motionless and unworn for nearly two weeks.

When I got back I gave it a few wounds and started wearing it. Within the first 3 hours or so it gained 7 seconds. I was surprised and a bit concerned. However, I continued to wear it daily for the next several days and it went back to only gaining about a second a day. Maybe closer to 2 seconds a day now. But pretty much back to its very consistent self.

My questions is, is this normal for a watch to sit unwound for a couple weeks to have a relatively large swing in time keeping within the first day of wearing it again? I'm tempted to just shrug it off and not think twice about it as long as it continues to be under 2 seconds a day. Just wondering if anyone thinks this is a known indicator of an issue or at least needing a service?

Maybe my GMT is just punishing me for not being taken along on the vacation?