THC withdrawals are caused by cannabis receptor downregulation that occurs when you stop using the drug. Its like any other downregulation WD symptoms you would get from, like, opiates, benzos, alcohol, coke, nicotine, speed, etc., etc. They all involve different neurotransmitters, but the principal is the same, you just need time to let your neurotransmiters readjust now that you don't have artificially raised transmitters from using everyday. Cannabis is one of the easier and less uncomfortable drugs to WD from.