natural ways to achieve unconsciousness

if OTC sleep aids won't work for you, and you can't get hold of a potent enough prescription drug, or can't manage to flush down enough alcohol, there's still some options left. to achieve unconsciousness.

eating a mouthful of yew seeds will do this for you. eating even more than that will kill you (see method 011)
you can expect to wake up, hours after your ingestion of a mouth-ful amount of these seeds, and suffer from
blood-circulation problems. that's what i got from my self-test. i was crawling around from room to room, because as soon as i tried to rise, i fainted. also, i threw up a lot. 1-2 weeks later eveything went back to normal.

another way towards a nap-attack might be via saliva divinorum

one of the plants Mazatec shamans use to facilitate altered states of consciousness. the active constituent here is a psychotropic molecule called salvinorin A.

according to Imanshahidi & Hosseinzadeh, by mass, salvinorin A "is the most potent naturally occurring hallucinogen." an effect starts to set in at doses as low as 200µg.

compare this to LSD, which is active at 20–30µg
-http://archneurpsyc.jamanetwork.com/article.aspx?articleid=652585

which is, admittedly, (up to 10 times) more potent, but synthetic and difficult to obtain.

salvinorin A is not note-worthily toxic. it's other use, besides inducing "hallucinations", might be to achieve unconsciousness.

"with very high dosage [...] either consciousness is lost; or at least one is unable to later recall what one is experiencing. the individual may fall, or remain immobile or thrash around; somnambulistic behavior may occur; injuries can be sustained without pain being felt; on awakening the individual will have no recollection of what he/she did, experienced or said"
-http://www.sagewisdom.org/faq.html

the question pertaining to the dosage now is: how high is "very high"?

this varies from person to person.

15mg salvinorin A, as it is sold in the form of 1g of dried leaves, is supposed to suffice for 15 (normal) uses for the average user.
-http://sagewisdombotanicals.com/

which can be smoked in tobacco pipes. "hold the smoke deeply in the lungs for a good 20 - 30 seconds 
before exhaling. this allows time for salvinorin A to be absorbed from the smoke. if one exhales to quickly, much of the material will be wasted"
-http://www.sagewisdom.org/faq.html

but as for the exact dose you'd need to achieve a strong effect, not much can be said. you'd have to try it out.

if you do successfully lose consciousness, "from beginning to end, the entire experience lasts 30 minutes to one hour."
-http://www.sagewisdom.org/faq.html

so, it's only useful in combination with toxins that take no(t much) longer than 30 minutes to kill. you can expect the onset of the salvinorin A effect 10-20min after oral consumption.

jateorhiza palmata, a lofty climbing plant, indigenous to East Africa. its root, calumba root, is being used by the natives as medicine. jateorhizine, columbamine, and palmatine are the alkaloids found in it.
"the alkaloids have a narcotic effect. they act similarly to morphine, increasing resting muscle tone in the smooth muscle of the intestinal tract [...] according to older sources, very high dosages can also lead to signs of paralysis and unconsciousness (Lewin)"
-"PDR for herbal medicine", p.208

to conclude this (the plant section), mandragora officinarum root extracts (see method 008) can also put you to sleep.

another reliable method of losing (and keeping sufficient distance to) consciousness is blood loss. a person carries around 6 liters of blood in his/her/zir body. substract 1 liter and you're there. substract another and you won't come back. it's been suggested to insert needles into ones veins and let the blood flow out. i tried
this to see if/how it works. it doesn't work (unless maybe if it is the femoral or jugular vein) one loses drop after drop with rather long intervals inbetween and it would take inconveniently long to discard enough blood for any sort of effect.

arteries (those that carry blood away from the heart) are under significantly higher pressure than veins (those that carry blood back to the heart). the (or in this case... my) arteria femoralis (a large artery inside the thigh) has been tapped during one of my stays at a hospital, to have my blood levels monitored. when i was about to get released, a nurse pulled out the needle (one of those puncture needles, around 5 or more cm in length) and mis-evaluated the amount of time that would have been needed for the injection spot to close itself, removed the medical cotton she held pressed there too soon, and i, in the twinkling of an eye, or literally in a heartbeat, got all covered in red. and actually almost blacked out.

the blood pressure in the arteria femoralis is enormous, and a small opening is enough to allow for a rapid blood loss.

"the femorals are the main arteries and veins to and from the legs. as you might expect, they carry a lot of blood, and an untreated cut to either one is quickly fatal. in one case, a thirty-four-year-old man bled to death from a 2 millimeter [...] nick to the femoral vein — and the vein is the low-pressure half of the circuit. they run next to each other, with the artery closer to the front of the leg, and are nearest to the skin at the groin, which makes a tourniquet hard to apply if that's the site of the cut."
-"suicide and attempted suicide" by Geo Stone, p.193