Dizziness and nausea after long ride

[Orion]

On Sunday I rode a 65km round trip on the Brisbane Valley Rail Trail. Total riding time was about 5.5 hours. That night I was tired but otherwise okay. On Monday morning I woke up feeling dizzy and nauseous. Initially I thought it might have been the chicken & salad roll I ate at the Blackbutt Bakery. However, since it lasted only about 2-3 hours I'm now thinking I may have overdone it on the ride.
I was hydrated well enough if the number of toilet stops on the way was anything to go by. I had one bottle (about 500ml) of hydralyte solution which I consumed about half of. The rest was water (about 2.5 litres). I also had a banana and two pieces of a muesli slice.
After the ride, for the rest of the day, I probably drank another litre or so of water.
I'm wondering if perhaps I needed to consume more hydralyte instead of just water? It was a reasonbly cool day so I didn't sweat too much.
I've been on a number of hard rides before but most lasted between 3-4 hours. I never experienced dizziness or nausea after those rides.
Can anyone offer any advice?
Thank you all.

[macca33]

Food, water (a lack thereof), or simple over-exertion - or a combination of the three perhaps.

[Orion]

Yes, I was thinking perhaps a combination of factors. Will have to remember to eat and drink more on extended rides.
Thanks for your replies.