At the end of the movie, we see Allie and Noah dead together holding each others hand. I think that Noah had been trying for a couple of times to let Allie remember everything permanently, but as he expected "miracle" did not happen a single time and everytime she lost everything. Now my question is how did they die together? As this was not the first time Allie forgot everything, I don't believe it was a serious physical problem that can cause death. Apparently, Noah was also not sick, although he got a heart attack but I believe it was out of his sorrow for again losing her. He was there to help Allie. So how come they died together? Did they commit suicide?
There is no mention of them committing suicide. The whole premise of the end of the film is that Allie remembered everything and that she and Noah died together at the same time because their love was so strong.