Sudden behavior chage - is this anxiety?

Question
About midnight last night my 3-yr old mixed breed (Border collie? Akita?) spayed female began restlessly pacing around the house from corner to corner, from crate to under a chair. She'll lie down, sigh heavily, rest for about 30 seconds to a minute then get up and pace again. Her posture is not quite "slinking," but her head is lowered, mouth open.  Her pupils are dilated. She has drunk water, gone  out to urinated once (I checked - there was pee on the ground), but she continues to pace.  Twice during the night when I sat near her she raised her head and whimpered.  She is not scratching, licking, or biting herself.  We treated her with Frontline yesterday at about 7:00pm (we treat her about every 6 - 8 weeks, have for 2 years, no adverse reaction).  Otherwise, no unusual events.  She is indoors and outdoors at will, runs around on our large farm - woods, fields, pond. Is this physical? emitional?  Would much appreciate any insight.  Thanks you.

Answer
Any symptoms such as you described need to be evaluated as emergent in the nearest emergency clinic or veterinary office.  This could be bloat developing; it could be some poison ingested outdoors; the result of an animal bite, an orthopedic injury you haven't witnessed occur, or any number of things.  I do not like Frontline; I've seen it cause serious injury (and even death) in dogs.  I understand the need to protect dogs (especially heavily coated ones) from ticks, but simply because the dog has never exhibited a reaction does not mean she won't.  The immune system requires several exposures to an antigen before demonstrating a negative response.  Take the dog to the veterinarian, even if she has subsequently recovered, and ask for medical advice.