लुङ्

The affix लुङ् (Aorist) comes after the verb in the sense of past time.
The लुङ् forms what is known as aorist. It is in fact the name of the aorist, as the whole of this affix is replaced by other personal terminations. See 3.1.43 and subsequent sutras.

The aorist has reference to a past time indefinitely or generally, without reference to any particular time. An action done before today is expressed by the perfect or imperfect; whatever remains for the aorist is, therefore, to express a past action, done very recently, say, in the course of the current day or having reference to a present act. Aorist, therefore, merely implies the completion of an action at a past time generally, and also an action done at a very recent time, as during the course of this day. The imperfect and perfect are used in narrating events of past occurrence, generally in remote past time; the aorist is used in dialogues and conversations which refer to recent past actions, but it is not used to denote past specified time or to narrate events.-- Apte's Composition. As अकार्षीत् 'he did'; अहार्षीत् 'he took'.

Vart:- The affix लुङ् comes after the verb वस् 'to dwell', when 'end of the present night' is indicated. Supposing a person rising from his bed at the proper time of rising (not in the middle of the night, but in the early morning) and finding another near him were to ask that one, 'where did you dwell i.e. pass the night'? That person so asked should answer in the लुङ् and not in लङ्. As अमुत्रावास्सम् 'I dwelt there'; and not अमुत्रावसम्.

Vart:- The above rule applies only in connection with waking after regular sleep. He who has not slept the whole night, but only for half an hour or so, should reply अमुत्रावसम्.