actually yes it is true, i've done it quite a few times... however, it's not like you smoke yourself to a point where you are sober as if you've done nothing that day.... your body/mind feels drain, but you're no longer high..

i suspect tho, it's just from smoking so much you can no longer get high for that day (or few days) and your high just wears off as it naturally would... so it's not really smoking yourself sober, it's smoking so much you just can't get high again for awhile....