My husband had this bounce at around that time and we were told it is perfectly normal and usually happens around that time.
We started at 3.74 (pre surgery) then went to 0.9 (post surgery) and then the dreaded bounce back up to 1.8 (gasp) and then back down and we were sitting at 0.39 at the last reading.
Trust me, I know it's scary but I had to believe the oncologist when she said "it's normal" to bounce around 18 months.
I hope that puts your mind at just a little bit of ease ...