What is the typical timing/content of your meals? Both can make quite a difference. Also, how long is it since you started your lifestyle changes? Most people have a "low carb" flu at times during the early weeks while the gut flora and hormones, enzymes, etc., adjust to radical changes in food content.

If you were using a lot of caffeine and stopped, that would take a while to stop affecting how you feel.

I'm assuming you made a lot of changes in what you're eating, and it's possible you accidentally started eating something that doesn't agree with you. Try eating a small number of trusted foods for a few days and see if you feel better, then add a food every few days to find the culprit.

things that make me feel like that:

If I felt hung over without drinking, I would (say it with me) spend more time drinking. Paying the costs, why not reap the benefits?

How much water are you drinking each day? Hangovers are mainly due to dehydration via the diruetic effect of alcohol. I've found that as long as I alternate one glass of water for every alcoholic drink I have (which isn't many) I have zero hangover the next day.

Do you feel better after you leave your house, and worse after spending a lot of time there? Did it worsen after the cold weather started (if you have cold weather)? Have you ruled out a natural gas leak or carbon monoxide from an improperly functioning furnace, water heater, etc.? A low level of chronic exposure could feel something like a hangover and might naturally feel worse in the morning after many hours of constant exposure. There may be other environmental factors. It might be worth at least making sure. I was having a similar problem and traced it to exposure to a theatrical hazer to which I was exposed 4 nights a week in a production in which I was playing.

Only happens to me when I have a sugar hangover, or if I'm traveling for some reason..

Any large dietary change will cause disruptions in your gut flora balance. Give your body a few weeks to adapt.

I felt the same way in the first few weeks of eating Paleo. It's most likely your body switching to a ketogenic metabolic state. I felt very foggy and bleary upon waking, and was very worried that it would persist. It did not.

The main things, as others have mentioned are meal timing, and water intake. I found that drinking more water during my VLC/ZC phase helped ease the transition, and skipping breakfast made all the difference in the world.

I also still sometimes feel this way if I eat too much sugar the night before, or if I've been lackadaisical on my Mg supplementation. Re-implementing it makes me groggy for some reason.

Henry, have you figured out a reason for this? I get the same thing and I can't find a dietary correlation. I'd actually say mine is worse than a "real" hangover, so if I've been drinking I feel better a couple hours after waking up. This phenomenon seems to knock me over for an entire day or longer.

Sometimes it happens after I don't get a lot of sleep, but other times it seems more out of the blue so I don't feel like I can blame it on a lack of sleep (at least not completely).

Did you change anything and notice any improvements? I'd love to hear a follow up! 8)

Heavy metal toxicity made me feel "hungover" for years(maybe even decades). Now that I'm finally on a consistant chelation program, the "fog/queeziness/dizziness/fatigue"" has lifted. It is quite remarkable.

How do you get rid of toxicity? My dr recommended the Paleo and I would say I am 80/20. I am still trying to wean out potatoes and such - but having a hell of a time! Lately, if I do drink - even a small amount- and even if I am not drunk, the next day I am VERY hung over. And if I don't drink, I sometimes feel hung over. My dr said its not normal but he has no idea why I'd be feeling like this (naturopath).

Once, while in ketosis, I ate a vine of grapes over the course of 2 days. I felt full on hungover and with impaired motor skills but without any feel good drunkenness for 36-48 hours afterwards. Knowing I had/have yeast overgrowth I attribute it to fermentation and subsequent methanol/acetaldehyde intoxication. Perhaps being in ketosis inhibited my sugar digestion? I was eating them throughout the day in small amounts, all day. I don't really know, just guessing. Other times I ate a high sugar treat without any effects like this, just a glucose spike and drop.