colon toxicity or leaky gut and lightheadedness

please does anyone know if when you take a good probiotic or start to increase your fibre intake..can it stirr up the rubbish and toxins in the large intestine..and cause you to feel light headed?

I am assuming this is because I have a leaky gut and the extra rubbish is getting back into my blood stream...and then my liver is being stressed trying to clean up the blood?

any thoughts please?

Thank you

ANNE