Anxiety can bring on a number of physical symptoms and one of them can be a feeling of fuzzy headedness or feeling overheated, sweaty and even nauseous. Stress is one of the main culprits that results in this type of anxiety reaction, so your sister had a good idea there.
Since you are going to see a specialist, be sure to bring a list of all your symptoms, when they happen and what happened just before and just after the symptoms. Often this can help pinpoint what might be causing this. If it's stress related, then there are a couple of things that you can do.
You do have young children and that, in and of itself, is stressful and quite demanding 24 hours a day. That's not to say you don't love your children, but you do need some time for yourself and some time to de-stress. If you haven't had this in quite awhile, then I would think that the stress is building up and, almost like a volcano, it bubbles up into anxiety symptoms.
What can you do outside of having your children taken care of by someone for a few hours a week? If that is not an option, then learn to use relaxation breathing (we have a video tutorial of this in our Tips column) and also do some mild exercise. The exercise that I'm thinking of can be done in the kitchen while you're doing meal preparation or cleaning up or even sitting in a chair for a few minutes. I do have a number of these exercises on my website on the Video page. Be sure to go through the videos until you find the exercise techniques.
You can do the relaxation breathing several times a day and it will help to keep the stress level down and will enable you to calm yourself. Of course, this is something that can be done by anyone and should be used whenever you might be feeling a bit upset and stressed or your anxiety level has gone up. Don't let the anxiety take hold of you before you use the breathing. Use the breathing to cut it off.
I hope this is helpful for you.