Going back to sleep after waking up once; sleeping in again.
今朝はアラームを止めて二度寝してしまった。
This morning I turned off the alarm and went back to sleep.
休日はつい二度寝してしまうことが多い。
On days off I often end up sleeping in again.
二度寝で遅刻しないように気をつけてください。
Be careful not to be late because of going back to sleep.