It is very common for an individual who is discontinuing any of the short-acting benzodiazepines might experience some sense of anxiety and some withdrawal insomnia after discontinuation.
The risk of addiction and dependence to Valium is very high, and the label on a bottle of Valium even says so.
Someone who takes antidepressants regularly and is going through withdrawal because of cessation of use will likely experience rebound depression, and may become more depressed than they originally were.
Large amounts of opiates, like heroin, can cause the respiration to shut down completely.