私はとても疲れていたのでぐっすり眠ってしまった。

I fell sound asleep because I was very tired.

私(わたし)はとても疲(つか)れていたのでぐっすり眠(ねむ)ってしまった。

Watashi wa totemo tsukareteita node gussuri nemutteshimatta.

私 (わたし、わたくし)

I; me; private affairs; personal matter; secrecy; selfishness

は (は)

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

迚も (とても、とっても)

very; awfully; exceedingly; (not) at all; by no means; simply (cannot)

疲れる (つかれる)

to get tired; to tire; to be worn out (e.g. of well used objects); to starve

ので (ので、んで)

that being the case; because of ...; the reason is ....; given that...

ぐっすり (ぐっすり)

sound asleep; fast asleep

眠る (ねむる、ねぶる)

to sleep (not necessarily lying down); to die; to close one's eyes

Readings: シ、わたくし、わたし

Meanings: private, I, me

Readings: ヒ、つか.れる、 -づか.れ、つか.らす

Meanings: exhausted, tire, weary

Readings: ミン、ねむ.る、ねむ.い

Meanings: sleep, die, sleepy