Some people use the terms the unconscious and the subconscious interchangeably, but this is not accurate from Freud’s definition.
Unconscious, first and foremost, does not mean, as it is used in medical terminology “knocked out” or anesthetized. In simple terms, the unconscious is the store of collected information that has been repressed and is not easily brought to the conscious mind. These memories not recognized by the conscious mind can be memories of trauma, or even simply memories, thought patterns, desires, and sense impressions that remain far below the accessible surface. Because they are in essence, inaccessible, they may drive and control the conscious mind on many levels.
The unconscious and the subconscious are vastly different. In contrast to the unconscious, the subconscious mind lies just below consciousness, and it is easily accessible if attention is paid to it. For instance, you might know someone’s phone number. This information is not stored in your conscious mind, but in your subconscious. If you think about it, you can produce the phone number, but it isn’t simply floating around in your conscious mind. You need to direct your attention to memory in order to remember the phone number. Those memories you can recall easily are not conscious unless you pay attention and focus.
When someone asks you to describe your perfect day, you reach into your subconscious mind for these memories. However, if someone asked you to describe the worst day you ever had, especially if it was particularly traumatic, you might not really be able to describe the worst. You’d be able to discuss memories in your subconscious that were memorably bad, but a truly traumatic day could be partly or completely repressed. In this example, the unconscious worked as a protecting force on the mind, even if this protection was wrongly guided. Really finding the most traumatic day of your life might require significant therapy to access layers of memory, which are deeply hidden, buried away from both the conscious and subconscious.
Also, the unconscious part of your mind is responsible for controlling most of the automatic physiological functions, like neurotransmitters and hormonal functioning. Some people argue that breathing and heart rate is partially controlled by the subconscious and partly controlled by the unconscious since, at times, we can have control over their function.