眠ってた

was sleeping, were sleeping

→ 眠る
眠っ sleep + て Te-form (conjunctive form) + た Past tense
verb · informal, imperfect tense Rare #33,025
was sleeping, were sleeping Colloquial contraction of 眠っていた.
JA: 昨日はよく眠ってた。
EN: I was sleeping well yesterday.
Conjugation of 眠る
Indicative imperfect
眠ってた

眠ってたのか?

Were you asleep?

— ライフ・イズ・ビューティフル (1997)

眠ってたんだ

I was asleep.

— グッバイ、レーニン! (2003)

よく眠ってたな

You were sleeping pretty soundly.

— プラットフォーム (2019)

眠ってたの

Were you sleeping?

— ふたりのベロニカ (1991)

眠ってたのね

You were asleep, huh.

— お嬢さん (2016)

それで――本当に三日もいなかったの?――一度を除いて、ぐっすり眠ってた

So—you really were gone for three whole days?—You slept soundly, except for one time.