Ben, this sounds very creepy but it would be helpful to know exactly how the fear manifests?

Is she now infected with other people's fears/nightmares/real life events? Hmm, no. It says her past.
Is she a grieving widow? Loss of a child?

When a grieving young woman undergoes an experimental group therapy for night terrors, she soon discovers that the treatment is worse than the cure when she starts to relive/ or, is haunted by past traumatic events.

Needs more consequences, but I need more info.  

I think the logline has sufficient engaging elements for pulling in a reader. Plus, I prefer my loglines to be as short as possible, especially in the thriller/horror genre.

My take would be:

When a young grieving woman, troubled by her night terrors, escapes from a mysterious clinic conducting eerie experimental treatment, her plagued past begins to catch up with her.

Hope this helps.

Thanks Yuvraj, that’s much cleaner.

LC - in terms of more info, the whole concept is this - the experimental treatment purports to be for treating night terrors, but that’s actually an initially unintentional side effect of the drug in development. The secret intention is to develop a a psych drug which makes problematic members of the population (the homeless, mentally ill, etc) more productive and effective workers (in a capitalist sense). The protagonist escapes because she suspects nefarious intentions (my goal is that the period of time before escaping the lab is hallucinatory and terrifying) and as a result of not being administered a full course, can remember embarrassing/controversial details. The pharmaceutical agency sends people after her but of course she isn’t believed and is perceived by her family, friends etc as paranoid and unwell.
  

I am taking liberties with your notion to come up with my own version, too obviously inspired by contemporary controversies, and I apologize already.

Genre: Horror
Logline: Impressionable teenagers strtessed by social media and environmental doomsdayers are convinced by scientist role models that they can discover and affirm their true humanity by removing a part of their brain and transitioning to a tranquil noble savage identity, only to discover as adults that the change is irrreversible, wreaking havoc with their lives and community. They must stop the mad scientists from creating more Neanderthals while hoping for some way to salvage their lives.