Year 12 for me was a blast for the first six months. Parties, slacking off classes, and ruling the school! I highly recommend it for anyone. On our last day of school (we had a few weeks of study break before end of year exams) we hijacked the assembly, chanted "Nana-na-na, Nana-na-na, Hey Hey Hey, Goodbye", and started a huge congo line before leaving!
As for the academic side, you definitely need to keep it up for most of the year if you are going to get anywhere. The stress is definitely there, but you've got to keep in mind that there is a four month break after so you may as well give it your all. No regrets. That was my motto for Year 12, and I offer it to you all.