Q. If one lost his place in SE, (shemone esreh), or is in doubt as to whether he may have skipped a bracha, what does Rav Miller shlita advise one to do? Repeat what he may have already said, or just keep on going?

A. Poskim disagree when a person was day-dreaming and lost track where exactly he is in the amida. Chayei Adam (24: 21) rules that he should return to the bracha that he is certain he has not yet recited. While Raban (179) and Kehilos Yaakov (Brochos 17) quoting Ohr Zarua, maintain he should go back to the brochos he is in doubt he has said. The reason is that we do not declare this to be a case of safek brochos or doubtful blessing, where we abstain of reciting them when in doubt, as the Chayei Adam claims. This is because we see all the intermediate brochos as a single one, and if you miss one, just continuing and reciting the rest would be in vain or a bracha lebatala. (See Minchas Yitzchok 5: 100). Ma’ase Ish (p. 88) and Bnei Re’eim (34) mention that the Chazon Ish would rule similar to the Kehilos Yaakov and repeat the doubtfully said brochos in order to continue with the rest of the amida. Ben Ish Chai (Mishpatim 20) also rules contrary to the Chayei Adam.
Harav Shlomo Miller’s Shlit’a opinion is to follow Chayei Adam rule and return only to the bracha that he is certain he has not yet recited.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a