The only times I've ever seen Nilla lying down is in the day(s) after getting vaccines. When I bought her, she was vaccinated the day before I picked her up and the previous owners had a hard time getting her to stand up in the pasture. She doesn't colic, she just seems to be exhausted. This year, she had the same reaction. Saturday - after vaccines on Friday - I turned her out to roll after lunging and she proceeded to roll and then stay down. I took pictures from a distance thinking she'd get up if I approached, but she didn't care. I eventually went into the ring with her and she enjoyed some scratches.
The vet had advised Bute for both Nilla and Shasta following their vaccines since they were both such assholes about it The vet said horses often have more reactions when they tense up. Shasta also ended up having to get all her shots on the one side of her neck instead of spread out because she tried to rear, strike, and trample the vet and me. In addition to regular spring shots, Shasta also got an ivermectin injection. I am really not a fan of doing these given the possible side effects, but it does cut down on her itching and keep her from scratching out her mane - which she has done twice before and I found a small chunk ripped out a week ago.
I came back Friday evening to check on them and found Shasta's neck already swelling. By Saturday the swellings were larger though my husband was convinced they weren't. We did call the vet and she recommended icing and continued Bute. Do you know how to ice a horse's neck? I don't. So I strapped a bag of frozen peas on with a polo wrap.
How Professionals Do It I'm Sure
By Sunday, her neck was massively swollen and I was starting to freak out. The vet recommended 25 Benadryl and more Bute for 3 days. Monday saw no reduction in size, but it wasn't bigger. And by Tuesday, the swelling was finally going down. I think we're going to need to space out her shots in the future. I also told my husband he needs to be there next time she gets shots. Shasta behaves for him.
Throughout all of these reactions, both Shasta and Nilla were eating (anything the could) and acting normal. Shasta really didn't seem at all bothered by the massive swelling on her neck. And we were following the vet's advice in dealing with the reactions. Nilla seems fully recovered and hopefully Shasta's swelling will finish going down.