Minecraft- Why has my horse suddenly gotten slow?

It's not the game that's slow, just my effin' horse. I've given it a rest and fed it golden apples/carrots but it's still slow. Dismounting and walking through water is faster than it is.

It must be a glitch, and you should try to save your world on restart minecraft.

I had this too. Some horses can usually be slower than others, but mine was thw fastest horse ever.
I woke up one day, and what do you know? I tried riding it. But even riding a PIG was the same speed as this. My bloody horse wasn't even injured or needed healing. I fed it too. NOTHING HAPPENED