My 6 year old, ridiculously confident cat, has been nervy for two days 
In 6 years she has lived with my dog (sadly pts last year) would try and go on walks with us and even if you made her jump the most you would get is a 'trill' in reaction. I honestly don't think the thought of something causing her pain has ever occurred to her!
Yet yesterday I went to let her in and she was really unsure of being in the house. Took about 5 attempts to get her to come in. Really jumpy all day. Looking outside all on alert etc. Then this morning she came into my room and snuggled under the duvet and slept over my arm. She has never done this. Ever.
Today she's the same. I'm assuming she got in a fight with a cat or a fox? She's eating and drinking normally and I cant see/find any injuries. She's just really really anxious.