I just got appointed head of Department

I just got appointed head of Department today. I am second in line for succession, going by seniority index of the Institution, not even the most senior. I had quite started looking for sabbatical outside Nigeria, I needed a new environment. This evening my HoD called me and said, congratulations, you’re our new HoD.
My initial reaction was a long noooooooo, but that’s how it is, for two year from this month.