This is the 5349th most frequent Japanese word.
nel
"Nel" is not a Japanese word.
Here, "寝ます" (nemasu) is the polite form of the verb "寝る" (neru), meaning 'to sleep', used to express a daily routine.
私は毎日午後9時に寝ます。
I go to sleep every day at 9 PM.
In this sentence, "寝ている" (neteiru) is the present progressive form of "寝る" (neru), denoting an ongoing action of sleeping.
猫がソファで寝ている。
The cat is sleeping on the sofa.
Here, "寝不足" (nebusoku) combines the kanji for 'sleep' (寝) and 'shortage' (不足), meaning 'lack of sleep', showing a derived noun usage of "寝る" (neru).