Sigh. This question is long and complex, so I will keep as short as possible right now and perhaps fill in gaps later as I go along.
Shortest answer: He has been suffering from post-surgery complications. He is having trouble producing red blood cells, even after several blood transfusions.
The reason that he had surgery is because, beginning in January, Kaesea started having bouts of vomiting (sorry -- this is kind of graphic) at intervals of 3-4 weeks. This was not any kind of normal cat vomit -- we're talking "lakes" of vomit (approx 2x2 feet in size -- a LOT.) After seeing his regular doctor the first few times it happened, we ended up going to see a specialist. And then things got nuts.
04/15 (Wednesday): Kaesea goes in for an ultrasound and endoscopy to take stomach and lower intestine biopsies. At that time, we find ulcers in his stomach and an enormous hairball. He goes home that night.
04/16 (Thursday): Over the course of the day, Kaesea looks worse and worse and is not eating. That evening, we take him to the vet and his temperature is 106 (normal for a cat is 100.5-1002.5). The concern is that one of his organs got perforated during the endoscopy, but ultrasound and x-rays prove that this is not the case. Kaesea stays overnight for fluids and meds to get his temperature down.
04/17 (Friday): Kaesea's temperature comes down and, over the course of the day, he looks slightly better. After careful evaluation, one of the vets speculates that the giant hairball found the day before may be causing his reoccurring issues -- perhaps it is floating in the stomach and occasionally becoming an obstruction, resulting in the large quantities of vomit. The plan is to do surgery to remove the hairball. On that day, I was reluctant because I wanted to take him home and get him healthier before proceeding with another anesthesia situation.
04/18 (Saturday): That morning, Kaesea looked really good. I talked it over with his surgeon and we agreed that we should go ahead with the surgery to remove the hairball. The plan was that he would be at home the next day, on the mend. Ha.
04/19 (Sunday): I got a terrible phone call that morning when I was about to check and see if I could pick him up. Not only could I not come pick him up, but his blood oxygen levels were at 9% (normal = 35% and his were 44% before surgery) and he needed a blood transfusion. We sat with him through his transfusion, which lasted for several hours. After the transfusion, his levels were 16%. Not great, but better than 9.
04/20 (Monday): Over the course of one day, his levels were back down to 9% and he had another blood transfusion. After the transfusion, he was up to 13. Then down to 11. Then 9. Again. At this point, he also had a couple of vasovagal episodes. (Basically, he fainted. But because his oxygen levels were so low, he also stopped breathing for a beat. In a nutshell: totally frightening freakout time.)
04/21 (Tuesday): Another transfusion in the morning. Same cycle all over again during that day. Bonus news: Kaesea the Vampire Kitty has used up all of the blood in the hospital. That evening, one of the vet techs brought in her own cat from home to be a donor. That cat's name is Boo -- we say that Kaesea got a transBoosion that night and boy did it ever go well: after getting some "Boo juice," Kaesea's levels were at 23%! Unfortunately, this day was also the 1 week mark since Kaesea had last eaten, which was getting to be a larger concern. On this day, we syringe fed him and he swallowed it all. So he got good blood and he ate. One of the best days of my life.
04/22 (Wednesday): Miraculous news -- Kaesea's levels went up to 25%. Wonderful, wonderful.
04/23 (Thursday): Levels back down to 23%. Still pretty great. Okay with 23.
04/24 (Friday): Levels down to 21%. Two tests done that day, eight hours apart. Both were 21%. Perhaps 21 is our sticking point?
04/25 (Saturday): Mid-day test comes in at 19%. Dammit. 1am test (after which I am now typing this) is also 19%, so it has held for two tests. Again. Another test tomorrow will show...?
[I will now commence daily posts, updating Kaesea's progress. If you've stayed with me this long, keep reading tomorrow for more...]