Anybody else encounter this? This is the third time this season I've experienced it; seems to be in cold winds.

• Weather conditions: high 20s / low 30s F; winds about 15-20 (I guess).
• Me conditions: jeans. long-sleeved cotton t-shirt. flannel-lined windproof jacket. wool or synthetic skullcap. windproof gloves. cotton socks and casual leather shoes. earbuds. lightly-loaded messenger bag. a little out of shape (but much better than this time last year).
• Bike conditions: upright 700c hybrid (Trek 7000). rack. one side pannier.

Hasn't proven dangerous, but has been disconcerting. I don't have any medical issues that would readily explain it, so I wonder if it has anything to do with exertion + cold winds.

Sure you have no medical issues? Sounds like a low blood sugar episode for me (I'm type 2 diabetic) More exertion the higher the likelihood it happens. Just throwing it out there. When it happens how do you alleviate it?

-Roger

Dehydration possibly combined with too much caffeine. Does it to me anyway.

Exertion in air temps that require slightly more effort , and topped off by a new cold season so our bods are not entirely used to cold riding yet. Add to that the new extra layers.... did you loosen the strap on your bag from it's warm season length? It could be too tight now. When the weather changes the effort goes up as the mercury goes down.

Take your pulse next time this happens. Too slow or too fast could explain your symptoms. As could a bunch of other medical problems. The list of things that cause diziness is long enough that I would not assume you don't have a medical condition, since this could be your first medical condition that is presenting as diziness.

You will have to exert yourself more strenuously in cold weather to achieve a given level of performance than would at a more comfortable temperature. Correct breathing can also be more uncomfortable, which might lead you to breathe less efficiently and get hypoxic--making you dizzy. Maybe you just need to back off a little and let yourself adjust to the seasonal conditions?

It's definitely not normal and is medical. Wether it's serious or not....????

All of the above are good guesses and you can eliminate those easily enough.

Could also be bad music.

Is your skull cap covering your ears? I've had this happen diving in cold water without a hood.....something about that cold hitting your eardrums.....or worse only one of them.

Good thoughts, all.
Not blood glucose levels: we have a family history of diabetes, so I'm familiar with what to look for there. The only beverages I had this morning were caffeinated (tea, not coffee). Had breakfast.
My breathing was certainly off today: struggling for breath and stopping frequently as I did when I first began this whole bike-commuting thing. (Years ago I used to get cold-air/exercise-induced asthma, so maybe that's recurring. Never associated it with dizziness before, though.) I was on city streets, not the MUP, so I was exerting myself much more than usual.
Skullcap covers the top of my ears, but not necessarily the ear canal or the entire outer ear. Maybe earmuffs are called for.

Maybe it's all of this combined?

Today was my first sub-freezing commute of the season, and I noticed a little dizziness too. I think for me it was a balance/equilibrium issue from my inner ears getting a little too cold.

Not getting sufficient oxygen will tend to make you dizzy, as can many other things, including but not limited to: dehydration, fatigue, lack of sleep, inner ear disorders, various types of illness, and certain drugs. It could be serious, it could be nothing much -- dizziness per se doesn't tell you.

As well make sure there isn't any water inside your ears from the shower before heading out into the freeze.