Flashbacks as part of PTSD commonly occur at night as one starts to relax and self distraction reduces, hence the high rates of initial insomnia, and substance misuse to induce sleep in PTSD. See also the poor sleep in borderline personality disorder. Panic during the day typically has an external trigger. In children night terrors and nightmares are part of the differential diagnosis.
I think the vestibular system is at the root of much panic disorder and nightmares. As this system is so intimately involved in sleep, there are likely to be differences in day and night panic attacks.
Nocturnal panic attacks are uncommon, but are generally present in people who have daytime panic attacks as well. In general nocturnal panic attacks are differentiated from disorders of arousal by the fact that when people wake up with a panic, they remember it, whereas in disorders of arousal they don't have recollection of it.
In addition nocturnal panic attacks are thought to occur in Non REM sleep. Please let me know if this was helpful