All inner resistance is experienced as negativity in one form or another. All negativity is resistance. In this context, the two words are almost synonymous.
Negativity ranges from irritation or impatience to fierce anger, from a depressed mood or sullen resentment to suicidal despair. Sometimes the resistance triggers the emotional pain body

Practicing the Power of Now: Essential Teachings, Meditations, and Exercises from the Power of Now (ed. New World Library, 2001) - ISBN: 9781577311959