They should've had Cuddy come over with some IV fluids, etc, to put him through Ultra-Rapid Detox. But yeah, it's odd and unlikely he "detoxed" inside of 12 hours. (When, again, in Season 1 he suffered for the better part of the week. Though he seemed to do it better then, maybe he was sneaking some then -prolonging his detox torture?)
The brain naturally produces a variety of opioid which interact with natural opioid receptors in the brain. The interaction between these natural opiods and the opioid receptors regulate a great many physical and neurological functions, including pain.
Opioid provided for pain relief produce a substantially more powerful reaction when they bind with the opioid receptors in the brain, compared to the opioid that the brain naturally produces. Furthermore, they are usually taken in larger doses than the brain naturally makes. In response to the effects of the opioid pain reliever, the brain cuts back on its production of natural opioid and reduces the number of opioid receptors that it has and the sensitivity of those remaining opioid receptors. This is why tolerance is developed. Dependency goes hand-in-hand with tolerance, because your brain has adjusted to the opioid intake such that it functions normally at the heightened opioid levels; the opioid produced by the brain naturally are no longer enough to preform their normal functions.
Withdrawal is from opioid is, simply, opioid deficiency, potentially lethal opioid deficiency. Which is why cold turkey is a stupidest thing that anyone can do. The gradual approach gives the brain time to build up new more sensitive opioid receptors and increase its production of natural opoids.
This does take time.
Quitting cold turkey and taking opioid blocking drugs makes it faster, because the brain's response is proportional to the severity of the deficiency, but that method is also fairly dangerous.
On the other hand, Vicoden is glorified Tylenol, seriously. Hydrocodone, the opioid present in Vicoden, is the crappiest of all the opioid pain relievers. It's almost totally useless, really. I speak from experience. The other component of Vicoden is common over-the-counter acetaminophen. For this reason, House's withdrawal symptoms and is likely to be significantly less than those of people who take the good stuff.
Of course, hallucination isn't a side effect of vicoden, so the whole thing doesn't make much sense. Good soap opera, though.
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