After people fall asleep, they sleep the deepest and most fragrant for the first hour or two, and then gradually become shallow. When they wake up, the inhibition of the cerebral cortex is very shallow. Dreams that happen at this time are closer to real life, and the coherence of dreams is sometimes stronger. After waking up, the short-lived image left in people's minds is clearer, so they can remember it clearly. Dreams that occur when you just fall asleep or sleep deeply are cold, messy and broken, and the cerebral cortex is suppressed for a long time. Wake up in the morning, often can't remember clearly.
In addition, we often see that what we remove is more exciting to us, but it is faint and vague in our dreams. For some things that we haven't noticed for a long time, we won't appear in front of us when we are awake, but when we are asleep, we may have a very clear image in front of us because of the weak stimulation, which is why some dreams are clearly remembered and others are not.