Valmiki Ramayana Ayodhya Kanda Sarga 28 Shloka 11
Original Shlokaसुप्यते पर्णशय्यासु स्वयं भग्नासु भूतले। रात्रिषु श्रमखिन्नेन तस्माद्दुःखतरं वनम्।।2.28.11।।
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स्वयम् on their own, भग्नासु broken (fallen), पर्णशय्यासु bed of leaves, भूतले on the ground, श्रमखिन्नेन exhausted with struggles, रात्रिषु at night, सुप्यते will have to sleep, तस्मात् therefore, वनम् forest life, दुःखतरम् is extremely painful.
Exhausted with struggles one has to sleep at night on a bed of leaves fallen on their own on the ground. Therefore, forest life is extremely painful.