I don’t know much about Epilepsy at all.

Epilepsy can be hugely varied from person to person. Seizures can vary from what you see in movies, to looking/acting like you're drunk, to looking like you're asleep sitting up, to a split second jerk of a digit, to an odd sensation and/or hallucination with no external symptoms. I've had the odd sensation, mine feels closest to dread but that's just me, the split second jerks, and I once had sustained jerking of my hands over several minutes. Also, IIRC only about 7% of the people with epilepsy are technically photosensitive.

But does watching this video have any affect on you?

If the room was dark and the flashing effected the majority of the light hitting my eyes, it would. Likely I'd just feel nauseated, a little light headed, and like a seizure was coming but I've never had light cause a seizure.

As I watched it in a bright room it had no effect on me.

Some videos have flashing light and Epilepsy warnings before them. Should this one have one aswell?

Need? Probably not given how the total brightness of the screen isn't changing that much. But it certainly wouldn't be a bad idea and as someone with epilepsy I'd certainly appreciate the heads up.