Symptoms of generalized anxiety disorder can vary in severity and may not be the same in all individuals suffering from anxiety. Common symptoms include restlessness, nervousness, worry, difficulty with concentration, feeling as if the mind is "blank," sleep disturbances, muscle tension, and fatigue. Anxiety symptoms can be associated with specific fears or phobias. There may be a tendency to avoid the object or situation that induces anxiety. Difficulty trusting others, startling easily, hypervigilance (excessive attention to staying safe), and nightmares are other possible symptoms. Severe symptoms are typical of those experienced in a panic attack and include palpitations, fast heart rate, chest pain, a sense of impending doom, shortness of breath, trembling, sweating palms, dizziness, feeling detached from oneself, nausea, and fear of losing control are all symptoms that may occur with a panic attack. Generalized anxiety disorder often occurs together with other mental health conditions. Sometimes, symptoms of one disorder may overlap with those of another disorder, or the disorders may be co-morbid (both present at the same time). Examples of conditions with symptoms that may overlap with those of GAD include obsessive-compulsive disorder (OCD), social anxiety disorder and social phobia, and posttraumatic stress disorder (PTSD).