Slow on Slow action

Do you know what happens when you cast Slow on your own Slow? I didn't. It's such a ridiculous idea but it is a legal play. Does the original Spell affected still go under the first Slow, which is now under the second Slow, or does it resolve normally?

If it does go under then does the first Slow resolve as normal and delay the original Spell in another turn? It seems like that'd be really weird because an opposing Caster trying to Slow your Slow would actually delay their own Spell by another turn.

Otherwise the original Spell was cast and only a Slow is under the Slow, so what happens when that first Slow goes back on the stack? Does it just fizzle? What if another effect played a Spell before the Slow resolves at the start of the turn? It seems unlikely but would the Slow get replayed and actually interrupt that Spell?

I've opted that the second Slow interrupts the first Slow interrupting the original Spell and that Spell resolves normally. The first Slow eventually goes back on the stack and likely has nothing under it and fizzles. I should ask an MZO about that.

Modern MTG clients must be a terrifying work of art behind the scenes. My head hurts.