Is it necessary to repeat Shemoneh Esrei if one pauses in middle?

In the view of the Shulchon Aruch, if a person takes a break for any reason in the middle of Shemoneh Esrei and the break extends for the amount of time it would take him to complete the entire Shemoneh Esrei from start to finish, he must start again. If the break is shorter than that, he must start again from the beginning of the brocha where he left off. Rema disagrees on the first point, holding that one only needs to begin again if he was forced to take a break. The Achronim disagree about whether, according to his view, the forced break must specifically be for halachic reasons. Practically, the Achronim rule that for Shemoneh Esrei, one must start over again even if his break was for non-halachic reasons. For other areas of davening, however, one would only have to start again from the beginning if the break was for halachic reasons.

סימן ק"ד ס"ה ס"ק ט"ז

Which brochos in Shemoneh Esrei are grouped together as one?

The Shulchon Aruch’s second point was that if the break was shorter than the amount of time it would take one to complete Shemoneh Esrei but it was in middle of a brocha, one would have to start the brocha again. This halacha only applies if the break took longer than the time it takes to say the brocha.  If it took less than that, one would just return to the point where he paused. If one paused somewhere in middle of the first three brochos, he must return to the beginning of the first brocha. This is because the first three brochos are counted as one brocha. A similar halacha applies to a pause in one of the last three brochos.  Many Achronim, however, disagree entirely with this point of the Shulchan Aruch. They hold that it is not necessary to repeat anything that was already said, unless the pause was for the time that it would take to compete the entire Shemoneh Esrei.

ס"ה ס"ק י"ז-כ'

Is one obligated to start over if he spoke in the middle of Shemoneh Esrei?

The halachos of pausing in the middle of Shemoneh Esrei also apply to one who mistakenly speaks in the middle of Shemoneh Esrei. According to some Achronim, making an incorrect addition to Shemoneh Esrei falls into the category of speaking during Shemoneh Esrei.  According to the opinion of Rema, talking is only a hefsek if one spoke under duress. If a person spoke deliberately, the Achronim disagree about whether he is obligated to start again -- even if he spoke just a few words.

ס"ו ס"ק כ"ג-כ"ה ביה"ל ד"ה דינו

• If a time-sensitive halachic question pertinent to one’s tefilla arises in the middle of Shemoneh Esrei, one may go to the place where the seforim are kept to search for an answer. If he is unsure of where the seforim are kept, he may go and look for a sefer.

• If a dangerous situation arises in the middle of Shemoneh Esrei, one should try to avoid the issue by walking away instead of interrupting his davening by speaking. Alternatively, if there is time before the situation turns dangerous, he can shorten his Shemoneh Esrei by reciting just the beginning and end of each brocha.

• Unless there is an important need, it is forbidden to step out of place in the middle of Shemoneh Esrei. If one did walk out of place, when he continues davening he should continue from the last word he recited. In the middle of Elokai Netzor, however, one may walk out of place even if a slight mitzvah arises.

• May one pause in the middle of Shemoneh Esrei to listen to Kriyas HaTorah?

• What is one’s obligation in davening?

• Are women obligated to daven?