to be lazy or slack; to become listless or languid — describes someone being idle or lacking energy.
週末は家でだらけてテレビばかり見ていた。
I lazed around at home and watched TV all weekend.
最近忙しくて、休みの日もついだらけてしまう。
I've been so busy lately that I end up feeling listless even on days off.
試験の後で友達がだらけているのを見かけた。
I saw my friend being slack after the exam.