I know what you mean. Pixel is the smallest dog I've ever had -- and my first Yorkie. She's just a little thing, 3 pounds at almost 7 months old, so I was really worried about her operation.
I took her in for 8am (sooo hard to leave her; I actually cried when I got back into my car) and her vet did some blood tests etc. to be sure she could tolerate the anesthetic. Sure, it cost more, but my baby is worth it and I would suggest it to everyone. Anyway, I called at 1pm to see how she was; she'd done well in surgery and was sleeping off the drugs. I was able to pick her up at 4:30 that afternoon. Little thing was soooo glad to see me that she literally climbed out of the attendant's arms and into mine.
She was very groggy and super sucky that night. Her stomach was upset from the drugs and we figured out, a day later, that she couldn't take the after-care prescription of metacam; poor little girl was lethargic and had a bad bout of diarrhea. I took her back to the vet and her prescription was changed to flagyl. It took another full day before her diarrhea calmed down. I kept pushing water and Pedialyte on her, afraid she'd get dehydrated.
She was spayed on a Tuesday and was completely back to normal by Sunday. She did have a rough time, and I was very worried about her for those days. She definitely needed extra love and attention -- she literally spent nearly 3 days in my arms, feeling miserable, poor thing. I've never felt so guilty in all my life. But it really was worth it for her. It prevents so many medical problems in future. To look at her now, bouncing around, playing and wagging that cute little tail, you'd never know she'd been so sick.