Anxiety can just hit you. Its weird. Ive had anxiety since I was 2 years old, so there was no reason for it to come...it just did. Anxiety can be caused by an imbalence of chemicals in your brain, and thats more likely the case with you if you havent experenced a major event. Maybe talk with a psychiatrist and see what they say. Shakey, light headed, fatigue...they all can definitly be signs of anxiety, but rule out any other causes which it sounds like your doing.
I wish you well
Does Anxiety really do this to you? YES, For sure it does. Anxiety can do so much to your body and mind. There are thousands of symptoms linked to anxiety.
Does this really happen even though I did not have a major event that happened around the time- YES, this can strick at any time in a persons life. Most people do not know what is wrong because of this. It is very normal to have anxiety, but you need to control it with meds or activitys like working out, running etc.
I would try some anxiety meds, ask your doctor for some to try out and see if they help you.
Anxiety is what it sounds like to me.
Hope this helps