Etymology
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sleep (n.)

Old English slæp "sleep, sleepiness, inactivity," from Proto-Germanic *slepaz, from the root of sleep (v.); compare cognate Old Saxon slap, Old Frisian slep, Middle Dutch slæp, Dutch slaap, Old High German slaf, German Schlaf, Gothic sleps.

Personified in English from late 14c., on model of Latin Somnus, Greek Hypnos. Figurative use for "repose of death" was in Old English; to put (an animal) to sleep "kill painlessly" is recorded from 1923 (a similar imagery is in cemetery). Sleep deprivation attested from 1906. Sleep-walker "somnambulist" is attested from 1747; sleep-walking is from 1840. To be able to do something in (one's) sleep "easily" is recorded from 1953. Sleep apnea is by 1916.

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sleep (v.)

Old English slæpan "to be or fall asleep; be dormant or inactive" (class VII strong verb; past tense slep, past participle slæpen), from Proto-Germanic *slēpanan (source also of Old Saxon slapan, Old Frisian slepa, Middle Dutch slapen, Dutch slapen, Old High German slafen, German schlafen, Gothic slepan "to sleep"), from PIE *sleb- "to be weak, sleep," which perhaps is connected to PIE root *sleg- "be slack, be languid," the source of slack (adj.). Sleep with "do the sex act with" is in Old English:

Gif hwa fæmnan beswice unbeweddode, and hire mid slæpe ... [Laws of King Alfred, c. 900]

Related: Slept; sleeping. Sleep around is attested by 1928.

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with (prep.)

Old English wið "against, opposite, from, toward, by, near," a shortened form related to wiðer, from Proto-Germanic *withro- "against" (source also of Old Saxon withar "against," Old Norse viðr "against, with, toward, at," Middle Dutch, Dutch weder, Dutch weer "again," Gothic wiþra "against, opposite"), from PIE *wi-tero-, literally "more apart," suffixed form of *wi- "separation" (source also of Sanskrit vi "apart," Avestan vi- "asunder," Sanskrit vitaram "further, farther," Old Church Slavonic vutoru "other, second"). Compare widow (n.).

Sense shifted in Middle English to denote association, combination, and union, partly by influence of Old Norse vidh, and also perhaps by Latin cum "with" (as in pugnare cum "fight with"). In this sense, it replaced Old English mid "with," which survives only as a prefix (as in midwife). Original sense of "against, in opposition" is retained in compounds such as withhold, withdraw, withstand.

Often treated as a conjunction by ungrammatical writers and used where and would be correct. First record of with child "pregnant" is recorded from c. 1200. With it "cool" is African-American vernacular, recorded by 1931. French avec "with" was originally avoc, from Vulgar Latin *abhoc, from apud hoc, literally "with this."

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sleep-over (n.)
1935, from verbal phrase; see sleep (v.) + over (adv.).
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hypnotic (adj.)
1620s, of drugs, "inducing sleep," from French hypnotique (16c.) "inclined to sleep, soporific," from Late Latin hypnoticus, from Greek hypnotikos "inclined to sleep, putting to sleep, sleepy," from hypnoun "put to sleep," from hypnos "sleep" (from PIE root *swep- "to sleep"). Modern sense of "pertaining to an induced trance" first recorded in English 1843, along with hypnotize, hypnotism, hypnotist, in the works of hypnotism pioneer Dr. James Braid. Related: Hypnotical; hypnotically.
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somniferous (adj.)

"sleep-producing," c. 1600, with -ous + Latin somnifer, from somni- "sleep" (from PIE root *swep- "to sleep") + ferre "to bear, carry" (from PIE root *bher- (1) "to carry," also "to bear children").

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hypnagogic (adj.)

"leading to sleep, inducing sleep," 1868, from French hypnagogique, from Greek hypnos "sleep" (see somnolence) + agōgos "leading" (from PIE root *ag- "to drive, draw out or forth, move"). Etymologically, "inducing sleep," but used mostly with a sense "pertaining to the state of consciousness when falling asleep." Related: Hypnagogically.

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hypno- 
word-forming element meaning "sleep," from Greek hypnos "sleep," from PIE *supno-, suffixed form of root *swep- "to sleep."
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insomnia (n.)
"chronic inability to sleep," 1620s, insomnie, from Latin insomnia "want of sleep, sleeplessness," from insomnis "sleepless," from in- "not" (see in- (1)) + somnus "sleep" (from PIE root *swep- "to sleep"). The re-Latinized form is from 1758.
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somni- 
before vowels somn-, word-forming element meaning "sleep," from combining form of Latin somnus "sleep, slumber," from PIE root *swep- "to sleep."
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