trembling and panting in dogs

[txdoggirl]

ok, I have an 11 yr. old chow mix...found out this past week that he's basically blind (but my Veterinarian thinks he can see light/dark), which I didn't know because I have 3 other dogs that he follows around...I knew he had slight cateracts (sp?) over the last couple of years...anyway, to my question...over the last week or so, at night-but not every night-he starts shaking and panting and basically acting like he's scared out of his mind...crawling all over me, etc. but then it stops after about 20 minutes...he's eating, drinking, etc. normally...could it be that he's just nervous as it gets darker because he can't see? However, the sun's not up yet and he's fine right now...any thoughts would be VERY appreciated....