context: Everybody gets the blues now and then. It's just part of life. But if you feel down or numb, or if your mood is getting in the way of your daily activities, you might have depression. Or you could have posttraumatic stress disorder ( PTSD). Depression and PTSD share some symptoms. With either one, you might have trouble sleeping, get angry over little things, or lose interest in people or things. Sometimes, you can have both conditions. Depression isn't something you can just snap out of. It's an illness that can be treated with medication or therapy. PTSD is an anxiety disorder that can happen to you after you see or experience a disturbing event, like war or accidents. Treatment can help with PTSD, too. It's possible to have just one bout of depression in your life. But for most people who have depression, it comes and goes over the years. It can take hold of you with no warning. But depression can get worse after you go through something stressful, like a divorce. It can last at least a couple of weeks, and the sadness or other symptoms affect you more days than not. You might: Feel sad or hopeless Get no pleasure from things you usually enjoy, like hobbies or sports Sleep too much or not enough Feel tired or lack energy, so that even little tasks take a lot of effort Have no appetite or eat too much Feel anxious or restless Have a hard time focusing your mind and making decisions Feel worthless and keep blaming yourself for things Think often about suicide or death It usually happens after you go through a life-threatening event or a long-lasting trauma, like sexual assault, domestic violence, or child abuse. If you see something terrible happen to other people, that also could cause it. Doctors, police officers, and emergency workers who deal with stressful situations regularly may get it. Signs of posttraumatic stress might start showing up a month or so after the event that sets it off. Or they might not come for years. PTSD symptoms fall into several groups: Unwanted memories. You might: Keep remembering what happened, even though that upsets you Have flashbacks, like you're reliving it Have an emotional or physical reaction when something reminds you of it Avoidance. You might: Try to keep from thinking or talking about what happened Stay away from people, places, or activities that remind you of it Negative thoughts and moods. You may: Be down on yourself, other people, or the world Feel detached from other people, hopeless, or emotionally numb Changes in emotional and physical reactions. You could: Be easily startled or frightened, or you might always be on guard for danger Do self-destructive things, like drinking too much alcohol or driving too fast Have trouble sleeping or concentrating If your symptoms go on for longer than 4 weeks, cause you a lot of distress, or get in the way of your home life or work, you may have posttraumatic stress. Some symptoms of depression and PTSD overlap. And you can have both conditions at the same time. Some, but not all, cases of depression can follow a traumatic event like a divorce or an illness. Some ways that the two conditions are similar include: Trouble sleeping or keeping your mind focused Lack of interest or pleasure in things you used to enjoy Irritability or bad temper Emotional detachment from other people If you have depression, PTSD, or both, treatment can help. To figure out what's wrong, start with your doctor. She may begin with a physical exam and rule out any other health problems. Then she may ask about your thoughts, feelings, and experiences. Or she might send you to a counselor. You have many options for treatment. Prescription medicines and talk therapy can work well. Some treatments can help with depression and PTSD at the same time. For example, a counselor can help you let go of negative thoughts and habits, and put positive ones in their place. If you feel so low that you think about killing yourself, get help right away. Call a doctor or counselor, or talk to a loved one or minister. If you or someone near you might be in immediate danger, call 911 or a crisis line right away. You can reach the National Suicide Prevention Lifeline at 800-273- TALK (800-273-8255).