Today after my set I felt like fainting, has something like this ever happened to you?

Hi guys! I swim every weekday around 2km-2.5km with a coach. Today for the last 400m I went a bit faster than usual and then I had to take like 5 mins in the shower because I felt dizzy and like I wanted to throw up.

I think I know the reason and it's that I hadn't eaten anything before training, I only had some high protein milk throughout the morning (1 liter, 46g protein).

It's the first time something like this has happened to me and I have trained before without having a full meal beforehand. Do you guys recommend eating before training? Or having something light instead of a full meal? Like some eggs and protein bar. I swim in the afternoons and the reason I hadn't eaten is I didn't have enough time to make lunch.