Malcolm Lader at the Institute of Psychiatry in London estimates the incidence of these adverse reactions at about 5%, even in short-term use of the drugs. The paradoxical reactions may consist of depression, with or without suicidal tendencies, phobias, aggressiveness, violent behavior and symptoms sometimes misdiagnosed as psychosis. Dangers of combining sedatives and alcohol
Sedatives and alcohol are sometimes combined recreationally or carelessly. Since alcohol is a strong  depressant that slows brain function and depresses respiration, the two substances compound each others actions and this combination can prove fatal. Worsening of psychiatric symptoms
The long-term use of benzodiazepines may have a similar effect on the brain as alcohol, and are also implicated in depression, anxiety, posttraumatic stress disorder (PTSD), mania, psychosis, sleep disorders, sexual dysfunction, delirium, and neurocognitive disorders (including benzodiazepine-induced persisting dementia which persists even after the medications are stopped). As with alcohol, the effects of benzodiazepine on neurochemistry, such as decreased levels of serotonin and norepinephrine, are believed to be responsible for their effects on mood and anxiety. Additionally, benzodiazepines can indirectly cause or worsen other psychiatric symptoms (e.g., mood, anxiety, psychosis, irritability) by worsening sleep (i.e., benzodiazepine-induced sleep disorder). Like alcohol, benzodiazepines are commonly used to treat insomnia in the short-term (both prescribed and self-medicated), but worsen sleep in the long-term. While benzodiazepines can put people to sleep, they disrupt sleep architecture: decreasing sleep time, delaying time to REM sleep, and decreasing deep slow-wave sleep (the most restorative part of sleep for both energy and mood).
A sedative or tranquilliser is a substance that induces sedation by reducing irritability or excitement. They are CNS depressants and interact with brain activity causing its deceleration. Various kinds of sedatives can be distinguished, but the majority of them affect the neurotransmitter gamma-aminobutyric acid (GABA). In spite of the fact that each sedative acts in its own way, most produce relaxing effects by increasing GABA activity.This group is related to hypnotics. The term sedative describes drugs that serve to calm or relieve anxiety, whereas the term hypnotic describes drugs whose main purpose is to initiate, sustain, or lengthen sleep. Because these two functions frequently overlap, and because drugs in this class generally produce dose-dependent effects (ranging from anxiolysis to loss of consciousness) they are often referred to collectively as sedative-hypnotic drugs.Sedatives can be used to produce an overly-calming effect (alcohol being the most common sedating drug). In the event of an overdose or if combined with another sedative, many of these drugs can cause deep unconsciousness and even death. Terminology
There is some overlap between the terms "sedative" and "hypnotic". Advances in pharmacology have permitted more specific targeting of receptors, and greater selectivity of agents, which necessitates greater precision when describing these agents and their effects:

Anxiolytic refers specifically to the effect upon anxiety. (However, some benzodiazepines can be all three: sedatives, hypnotics, and anxiolytics). Tranquilizer can refer to anxiolytics or antipsychotics. Soporific and sleeping pill are near-synonyms for hypnotics.