I accidently logged off my computer, and when I logged back into minecraft, all my achievements were gone. Pls help retrive my achievements again.

This appears to be a duplicate of MC-187701, which hasn't yet been resolved. If you have any additional information to provide regarding this issue, feel free to comment on the parent ticket. If you feel that this issue is affecting you, feel free to vote for the duplicated ticket, to give Mojang a basic idea of how many people are impacted by the problem. Just to further inform you, this will not determine how quickly the bug gets handled or fixed.