cat behaviour question - sudden biting, seemingly no trigger

so far i haven't been able to explain this well to other people / heard of cat owners encountering the same thing, but i'll try and describe it again in this post...

as an introduction, Biscotti (my cat) is not an agressive cat, she's very much a "flight" response type of cat in the "fight/flight" dichotomy when animals are stressed/scared. 

anyhoo. sometimes when i'm with her (eg. sitting next to her, her on my lap, patting her, or not patting her - basically not any one particular scenario) i can feel like her personality or mood "flips", and she suddenly looks at me with non-blinking eyes, pauses and seem to be concentrating on biting me. now, i have to explain that when she's doing this, her ears and tail are in normal position (not like when cats are in a fight), and her bites are not quick and penetrating, it's more of a gnaw...freeze/pause... gnaw... freeze/pause. So basically when it happens i just feel really weird and uncomfortable, cos it's not like i can feel her being angry and scared, it's just a zombie-like/action that doesn't seem to have a clear motivation. (it's hard to explain an 'intuition' / a feeling...)

and usually when i say no and point my finger sternly towards her nose she backs away/flattens her ears/looks away, but when she's in this "mode" she doesn't show any fear and just remains put in her spot with the same stance and still maintaining eye contact with me. and another thing that scared me when i first noticed this behaviour was that she'll even start to raise her body up and move in sudden movements towards me - like trying to dominate the situation (but her ears are normal! i can't tell what she's thinking!). as her owner, this is very uncharacteristic - she is NEVER bite-y. and though she's a really flighty cat, it's never when it's just me around her. 

and similar to how it started, she also snaps out of this unusual behaviour without any obvious environmental triggers either... and just resumes to being her normal, relaxed self.

so yeah, i'm just wondering if anybody knows any other information regarding this weird behaviour? it just suddenly happens seemingly without any trigger. and it happens quite infrequently - probably 3-4 times in the last 1-2 years.