Did something spook him? I got caught in a fireworks display with my three and I just went through the same exact problem with my Greyhound Athena, after. What worked was going back to crate training. We hated to do it but that was all that worked (and we tried everything, even buying a Thundercoat). We dragged her out. ( and head leader makes this easy) and made her stay out till she made. or we ran out of time and she went in the crate. Once she made outside, she got to stay out of the crate. It took a about a week.
She still had outside fear issues, but has been getting over them, a little at a time. Now it's mostly just loud noises that scare her.