Right now, Rei and I are staying in a monthly apartment in Ota-ku (think "southern Tokyo"), down by Kawasaki.

They call monthly apartments マンスリーマンション (mansurii manshon).

Please don't ask me why in the world a nice, new apartment in Japan is called a "mansion," a マンション (manshon), while a small, usually older building is called an アパート (apaato), an "apartment."

Google images makes this distintion very clear.

マンション (manshon):

アパート (apaato):

アパート (apaato), by the way, is short for アパートメント (apaatomento).

Anyways, we're in a マンスリーマンション (mansurii manshon).

And most days, I wake up at 5:30 a.m. and write these emails before I do anything else (i.e. my real job).

But today, alas, I overslept:

寝坊した。
nebou shita.
I overslept.

The main reason is that I was up all night reading nerdy fantasy books on my Kindle...

夜更かししちゃった。
yofukashi shichatta.
I stayed up late.

Note that in this second one, instead of saying した (shita), "(I) did (oversleeping)," I wrote しちゃった, which is the casual form of してしまった (shite shimatta)/ してしまいました (shite shimaimashita).

して is te-form of する, "to do."

しまった (shimatta) / しまいました (shimaimashita) is the past-tense of... しまう (shimau), "to put away; to finish"

Anyways, the nuance is that I wasn't intending to stay up late, wasn't supposed to stay up late, but... oops, I did.

As a result, I didn't write this email at my desk at 5:30 a.m. I'm writing it at 11:36 a.m.

...and falling behind on work 38 times more boring than this.

頑張ろう。
がんばろう。
Let's do our best.
Literally: There's no good translation for 頑張る.

Bonus Phrases:

マンスリーマンションって超便利。
マンスリーマンション　って　ちょう　べんり。
Monthly apartments are so convenient.
Literally: monthly mansion + って + super-convenient

新築マンションがいいです。
しんちく　マンション　が　いい　です。
I'd prefer an apartment in a new building.
Literally: new building + mansion (=apartment) + が + good + is

今アパート探してるの。
いま　アパート　さがしてる　の。
I'm looking for an apartment.
Literally: now + apartment + am looking + の
Note: This の at the end of the sentence sounds feminine.

アパートメントの略がアパートだよ。
アパートメント　の　りゃく　が　アパート　だ　よ。
"Apaato" is short for "apaatamento."
Literally: apaatomento + の + abbreviation + が + apaato + is + よ

無駄遣いしてしまった。
むだづかい　して　しまった。
I wasted my money.
Literally: wasting + did
Note: I'm guessing "money," since we don't have context here.

また同じ間違いをしてしまいました。
また　おなじ　まちがい　を　して　しまいました。
I made the same mistake again.
Literally: again + same + mistake + を + did