Howling:Amy's Choice - Why wouldn't the doctor just die?

I was watching some Series 5 recently and...

In Amy's Choice, the Dream Lord threatens The Doctor, Amy and Rory with a deadly danger in two very realistic 'states'. they must choose which one is a Dream and which one is reality. If they die in the dream, they wake up. BUT! they must be careful... As if they die in the wrong 'state' and it turns out to be reality, they would die.

What I don't get though, is why didn't the Doctor just kill himself in either 'state', because after all, if he died in the dream he would wake up and be able to wake up the others, but if he died in reality, he would regenerate! So he would save his two companions at the simple price of one incarnation, which would, be inevitable as he would regenerate eventually anyway! If he did pick a 'state' to die in, I'd pick the one where Amy is married with Rory, and is pregnant.