A significant number of patients are afraid of the nighttime and do expect a loss of control or severe somatic consequences like a heart attack, stroke or other irrational cause of death. Of course this is most unlikely!
We know that most panic attacks are NOT caused by dreams. Records of sleep polysomnographia show a maximum of panic attacks during early sleep phase (phase II), not during the REM-phases associated with dreams. This is a major difference to nightmares! Nightmares happen during the second half of the night, so we are often able to remember the content of these dreams.
Pavor nocturnus is a very specific type of sleeping disorder, more common among children. It is defined by a sudden avakening with crying, strong anxiety symptoms and vegetative symptoms like heart palpitations, short breathening and sweating. This type of sleeping problems occur during deep phases of sleep (phase IV).
Arousals caused by sleep apnea syndromes are usually not characterized by extreme anxiety symptoms. But this sleep disorder might have an effect on the origin of panic attacks, because sleep apnea has an impact on heart frequency and blood pressure. Chronic arousal of anxiety during night could be a kind of dysfunctional protection against apnea during night.
The exact causes for panic attacks at night are not known. Other possible causes include an increase of CO2-concentration (False Suffocation alarm hypothesis) or changes of the parasympathotonic system due to autonomic dysfunction.
So panic attacks at night will be mainly influenced by the events of the last day, consumption of alcohol or drugs and a general higher arousal due to the anxiety disorder of the client.