〜まま: leave a state unchanged
Describe a resulting state or an unperformed action that remains unchanged. Distinguish a maintained state from simultaneous actions.
Maintain the state after a completed action
靴を履いたまま部屋に入りました。 means entering the room with shoes still on. Putting them on happened earlier; the resulting state continues.
窓を開けたまま寝てしまいました。 likewise means falling asleep with the window left open. Opening it and sleeping are not simultaneous actions.
Use negative forms and noun phrases
朝ご飯を食べないまま出かけました。 means going out without having eaten breakfast. まま can follow the negative ない-form too.
このまま待ちましょう。 suggests waiting as things are. Nouns connect with の, as in 私服のまま for remaining in everyday clothes.
Separate a state from an ongoing action
座ったまま話します。 means speaking while remaining seated. By contrast, 音楽を聞きながら話します。 presents listening to music and speaking as two actions in progress at the same time. Distinguish a maintained state from simultaneous actions.
まま does not always imply a mistake or a bad situation. そのままで大丈夫です。 says that things are fine without a change.
Quick check: In コートを着たまま休みました, did the person take the coat off before resting?
Show the answer and why
No. They rested with the coat still on. まま maintains the state resulting from 着た.