Low mood and depression can feel close from the inside. Both may involve sadness, tearfulness, reduced energy, irritability, concentration difficulties, poor sleep, withdrawing from other people or losing interest in things that usually matter. It is understandable to want a clear line between them. In practice, that line is not a self diagnosis test and a webpage cannot decide which description fits one person. Low mood can be a proportionate response to disappointment, loss, stress, conflict, physical illness, financial pressure, caring responsibilities, a major transition or a difficult period. It may fluctuate with circumstances and ease when the pressure changes or when someone has support and rest. Depression can be a more persistent and wide ranging pattern that affects mood, motivation, hope, enjoyment, sleep, appetite, concentration, movement and day to day functioning. Some people experience depression without describing themselves as sad. They may instead feel numb, flat, exhausted, unusually guilty, disconnected or unable to get started. Duration matters, but it is not the only consideration. A short period can still feel serious and a longer period does not prove a particular diagnosis. The impact on daily life, the pattern over time, physical health, medication, substance use, sleep, recent events, safety and personal history can all be relevant. A qualified clinician or GP can consider the wider picture and decide whether medical review, psychological support, practical support or another response may be useful. Physical symptoms should not automatically be attributed to mood. Fatigue, sleep changes, appetite changes, pain, slowed thinking, agitation, concentration problems and changes in motivation can have physical, medication related or psychological contributors. New, severe, persistent or worrying symptoms should be discussed with an appropriate medical professional rather than explained away by anxiety, stress or depression. It may help to notice a few things before a professional conversation: when the change began, what has been happening around it, whether enjoyment has altered, how sleep and eating have changed, what daily tasks are harder, any relevant health or medication information, and what support has helped even a little. These observations are not proof of depression. They simply provide useful context. CBT based therapy may be considered when appropriate after assessment. It can explore the interaction between mood, thoughts, avoidance, routine, relationships, self criticism, activity, sleep and the pressures around someone. It is not a replacement for medical assessment, medication advice, social support or urgent care. Where behavioural changes are useful, they should be collaborative and realistic, not a demand to push through exhaustion or to follow a rigid programme alone. Urgent support is important if someone has thoughts of suicide or self harm, feels unable to stay safe, has stopped caring for basic needs, is experiencing psychosis, severe agitation or a sudden marked change in their mental state. A guide cannot assess immediate risk or create a crisis plan. Seek urgent appropriate help in those circumstances. For related information, see depression support at lyceumclinic.co.uk/therapy/depression/, the guide to CBT and depression at lyceumclinic.co.uk/guides/cbt for depression evidence/ and the guide to depression and burnout at lyceumclinic.co.uk/guides/depression vs burnout/. If you want to explore whether CBT based therapy is suitable, you can enquire about current arrangements and availability. When someone is unsure what to say, a simple starting point is enough: what has changed, how long it has been difficult and what feels hardest right now. Assessment can begin with the person’s experience rather than a perfect description.