Experiencing or witnessing upsetting events can lead to post-traumatic stress disorder (PTSD), a mental health condition that affects 7.7 million American adults. The disorder can cause people to feel anxious and afraid, leading to flashbacks and nightmares. In fact, up to 96 percent of people with PTSD have these upsetting dreams. Fortunately, there are several approaches to treating PTSD-related nightmares. If you or someone you love is dealing with PTSD, read on to understand how it impacts sleep, and available treatment options.