Serious reaction to being awakened

I'll start with a brief question:  my adopted 5 year old M Pembroke has been with me for 10 weeks but (yes, let sleeping dogs lie) when aroused or disturbed while in what my trainer calls "rem sleep" he becomes threatening....growling and (believe it or not) stalking me throughout the house.  It's Jekyll and Hyde.....he appears to be in a zombie state.  When the incident ends maybe 10 minutes later he appears shamed, sad and wanting affection and cuddling.  I've got a lot of other loose ends about Sammy but I'll throw this one out first.....

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    Amber and Kirby

    I would go in for a vet visit to rule out a medical or neurological issue. Preferably a veterinary behaviourist.