While you might be feeling hungover, I think the main reason you probably feel the need to take it again is acute withdrawal as it leaves your system very rapidly. You're probably getting rebound anxiety and a slight increase in all the symptoms that phenibut helps counteract when you're on it. I definitely wouldn't call it addiction. In fact, maybe your dose is a bit on the high side given your tolerance so the acute withdrawal is particularly noticeable. Everyone has different neurochemistry so I wouldn't take the guide as the perfect advice for everyone. In fact the guide is probably trying to encourage people to play things as safe as possible. Considering how long-term phenibut withdrawal can be pretty bad, I can see why it wouldn't suggest people to take it for a second or third day in a row - but if that's worked best for you, then don't deviate from it.

If this is an issue you wanna avoid going forward, I would maybe take lower doses, because that will obviously make the hangover and acute withdrawal less difficult. Perhaps see if you can go taking it just once at a time (not on subsequent days) after a slightly lower dose? Then you'll be able to tell if that's the issue.