bichon behavior changed

Question
my dog always slept in bed with me, now he runs into other bedroom and goes under bed and can't get him out for hours....he also started barking more than he ever did...any help will be useful, they say there is always a reason why a dog will change.

Answer
We can't know for certain if this is truly behavioral or a byproduct of some unknown biologic cause.  First stop: veterinarian, full blood chemistry (expensive), complete examination (orthopedic, opthalmological, auditory, and base line neurological).  Make the other bedroom inaccessible (close the door).  Do NOT pursue the dog to attempt to persuade him back into your bed.  This will worsen the response if it is a fear response (behavioral) to something that occurred to him while you were sleeping (sound outside, your turning over and possibly harming him without ANY INTENTION, etc.)

Let's see what the veterinary results are.  Meanwhile, the barking also indicates there might be either a biologic cause (no idea how old he is, temporal lobe seizures can occur at any time in a dog's life but are usually seen between 18 months and 4 years of age) or an external stimulus.  Ignore it.  Don't attempt to calm him, don't tell him to stop, simply LEAVE THE ROOM for ten seconds every single time he demonstrates over barking when there is no apparent (to you) cause.  Reward his silence.  When he has voluntarily STOPPED barking, say "quiet" and toss a high value treat to him (in plain sight so he sees it immediately).  You are then creating a conditioned response to the word "silence" and high value reward.  Over approximately 30 to 50 repetitions, the dog should begin to respond to "silence" by not making any sound (providing there is ABSOLUTELY NO CAUSE) and reward.  Re-post with veterinary results using followup feature so I can see original question, answer.  Thank you.