If one has a safek if he skipped a bracha in S”E (due to spacing out during davening), does he need to repeat S”E, or is there a chazaka that he said everything correctly? What about if he already stepped back?
If one already finished davening and has doubt if he skipped a bracha, he can rely on the fact that he presumably davened as he usually does and did not skip. However in this situation he can daven a “tefillas nedava” a voluntary tefilla, as long as he adds additional personal supplications in his shmonah esrei.
See O:C 107:1 that one who is doubtful if he davened must daven again and stipulate that if he is not obligated [if he actually davened]. This is because of Rav Yochana’s opinion that “one should daven the entire day” [the commentaries explain that without this reasoning we would be lenient on grounds of a Rabbinic doubt].
However, this is only one who does not know if he davened at all. One who davened and is not sure if he did so correctly seems to have a different ruling, that we rely on his “chazaka” standard practice. See Rama 422:1 who rules that one who is doubtful if he said Yaale Veyavo need not repeat Shmone Esrei, the Mishna Brura explains that this is due to the fact that we do not go 30 without saying Yale VYavo and so have no chazaka not to say it. The halacha does not follow the Rama. The Mishna Brura explains we assume a person prayed as normal without Yalle Veyavo.
This is also the ruling with regards to Mashiv Haruach and Vsen Tal Umatar, see Shulchan Aruch and Rama 114:8, that we establish a chazaka based on a 30 day period of davening one way. Hence, one who would certainly have a chazaka he davens as he normally does. Although we generally do not encourage tefillas nedava it would seem in this instance it would be ideal to daven a nedava with a stipulation.
see Pesach Hadvir O:C 209:2