Hi Nick,
I experience all of those symptoms on an all too regular basis.
I get two kinds of headaches, one I am familiar with from before the accident, called a tension headache. The second type feels like my brain is struggling too hard. The latter I take as a warning that I'm trying to do too much and I slow down or rest once I start to feel it.
I also take dizziness as a sign that I'm overdoing it.
And fatigue it yet a third signal that overdone it and that I need to rest.
If you feel those at the top of a walk again, I recommend that you try to pace yourself and the energy you have for the rest of the day instead of going on the walk. I have found that doing that for myself helps me to not push myself too far in a day.
When I trust those signs when they come and don't push myself too far for longer periods of time, I do better cognitively. When I do better cognitively, I feel better emotionally. And maybe that will work for you too.