"Lingering fear" is when after a fearful/traumatic experience, you still have some fright remaining despite there are no more dangers. I was wondering if there's any single word that can possibly represent this?
Residual Fear, vestigial and impending;
If the fear is pathological, then the given answers, neurosis (Charon) and PTSD (Centaurus ) would be best to describe the psychological trauma.
But the fear experienced in everyday life may be unpleasant but not damaging. Such fear, if it is a vestige, is experienced as (Oxford definitions)
If there is also menace of the fear returning there is, (Merriam-Webster definitions)
'foreboding(presentiment especially of coming evil),'
'trepidation(: a feeling of fear that causes you to hesitate because you think something bad or unpleasant is going to happen),'
'edginess'( characterized by tension) may be experienced.
Clearly a widespread experience, and there are many shades of meaning to choose from.
The best term for that condition, as mentioned above by FF, is PTSD which stands for "post-traumatic stress disorder". The term describes exactly what you mentioned and there is no single and specific word for that.
- Posttraumatic stress disorder is an anxiety disorder that can develop after a person is exposed to one or more traumatic events, such as major stress, sexual assault, warfare, or other threats on a person's life. Symptoms include disturbing recurring flashbacks, avoidance or numbing of memories of the event, and hyperarousal, continue for more than a month after the occurrence of a traumatic event. - Wikipedia
I think that neurosis fits your requirements quite well.
A relatively mild mental illness that is not caused by organic disease, involving symptoms of stress (depression, anxiety, obsessive behaviour, hypochondria) but not a radical loss of touch with reality.
(in non-technical use) excessive and irrational anxiety or obsession.
Whilst it isn't exactly synonymous with 'lingering fear', I think that someone who did have a recalcitrant, irrational fear could be said to be neurotic.