It is no coincidence that the Western symbol for 'male' is a「raised arrow」(♂) just as this Chinese glyph meaning ARROW also refers to the MALE PENIS and any other「penetrating shaft with a head.」…Note that the Western symbol for 'female' uses the Chinese glyph「full screwing below orifice」(♀), perhaps for similar reasons.
「Laid out flat with two hands」suggests a person grasping the shaft of an ARROW after being felled by it (perhaps the target was struck in the front of the torso, a place more than others to cause fatality and therefore often the aim of archers).
「Head sliding in heaven」: Chinese glyphs often depict a clear analogy of bow and arrow weaponry with a client using a service provider: the inner foot arch and arched shape of the archery bow (弓「end-to-end, side-to-side with no-longer-integrated foot」) in use with an arrow (the penis 矢「head on taut thrusting shaft」or「head with heaven, heavenly head」) drawing back and forth nocked in a bound string (糸「stringy emissions from rod, loose and dripping with small youth」) for discharges (放「person coercion, side method for prostrated whacking」).
To VOW or to SWEAR to do or not do, or to tell the truth and so on, can all be readily related to illnesses of one's penetration weapon, dart, sharp-tipped shaft, and one's various「head(s) in heaven.」
Arrows were carried in quivers, normally slung on a belt and hanging down from around the waist in China as does the male member, or dangling from one's mount while riding, and not between the shoulder blades as was the style in the Americas. See the related glyphs that equate arrows and shafts, quivers and quivering, bows and bowed over with sexual activity, and being close to heaven and meeting various gods due to both grave illness and/or great ecstasy.
「Prone and spread big」or「head in heaven.」…and of course if a person's head is in heaven, the person is either dead or engaged in some sort of intercourse. If lying prone and spread-eagled, then the person is either shot or deadly ill, or engaged in some sort of intercourse. Original glyph meaning「heaven」(䒶) uses elements of「emerging shafts pulled, dragged, or jerked back taut」depicting some sort of a PIERCING SHAFT, and with an arrowhead and fletching attached describes an ARROW.
Elements are also「head」on「downward thrusting shaft to one side」of a bow, and「taut」while nocked on the bowstring and held back by the archer's hand. VOW and SWEAR as one's「head in heaven」where the spirits are listening and watching, much as Santa Claus might do.
When used as an element, also refers to a DISEASED PENIS (see Used-In glyphs), referring to any situation or conditions that SEXUAL INTERCOURSE IS NOT PERMITTED or is LIMITED, most likely after having become infected. Sexually transmitted diseases have the tendency to curl, bend, and shorten a penis, often pulling it to one side. A DISEASED PENIS also is a「head on downward thrusting shaft」with fluff at the base,「positioned to one side」when「taut.」
Both an arrow and a diseased schwantz can cause damage by penetrating a body. Gonorrhea and other such diseases can cause scar tissue to form within the urethra, causing a bent penis, especially when erect:「Peyronie's Disease,…also known as 'Induratio penis plastica,' or more recently 'Chronic Inflammation of the Tunica Albuginea (CITA),' is a connective tissue disorder involving the growth of fibrous plaques in the soft tissue of the penis affecting up to 10% of men. Specifically, scar tissue forms in the tunica albuginea, the thick sheath of tissue surrounding the corpora cavernosa causing pain, abnormal curvature, erectile dysfunction, indentation, loss of girth and shortening. …The disease may cause pain. Hardened, big, cord-like lesions (scar tissue known as 'plaques'). Or abnormal curvature of the penis when erect due to chronic inflammation of the tunica albuginea (CITA). Although the popular conception of Peyronie's Disease is that it always involves curvature of the penis, the scar tissue sometimes causes divots or indentations rather than curvature. The condition may also make sexual intercourse painful and/or difficult…」
[ https://en.wikipedia.org/wiki/Peyronie%27s_disease 2012-08-15 ] perhaps the source of the English epithet,「get bent.」

External source definitions …excluding politically incorrect concepts and other meanings deemed offensive today; may include extended definitions, euphemisms, and mnemonics)
Chinese: arrow; dart; straight; to vow; to swear
Japanese EDRDG: dart, arrow
Unihan extended: arrow, dart; vow, swear