A good head after primary??

[Sheepy]

I bottled up a batch of honeyed lager made with ale yeast last night in 2l PET bottles. All my previous brews (admittedly only 3) have remained quite flat. However on bottling (tube from tap into bottles) the brew real fizzed up and created quite a head. This subsided as i got further through the bottling. Is this going to be ok, i figure the fizz is trapped CO2 and this will have pushed ant O2 out of the bottles so cant be that bad.