I recommend that you experiment with a simple practice for a few days. This will lead you enjoy complete rest during sleep and feel active and energetic upon waking. At that point, the answer to the question why this happens will become clear out of an inner realisation. The second way is to explain the reason why this happens so that you have a conceptual understanding of the theory behind your actual physical experience and then start finding our what needs to be done to change your morning experiences.
Since you are asking this question for yourself and not for helping someone else who is going through this experience, I shall confine myself to the first way. I have seen that usually conceptual understanding causes an additional barrier to experiential realisation. Whereas experiential realisation not only heals but also gives rise to conceptual understanding with ease.
There are three simple things I suggest you do before going to sleep and immediately after waking up. All these three activities together would take about twenty minutes. At bedtime, you need to do these three things just before sleeping so it would be good to switch off bright lights and all electronic devices (TV, Laptop, Tablets, smartphones, etc), visit the toilet and not do anything else after these three activities. In case you are unable to fall asleep, you can repeat the last activity until you fall asleep. Similarly in the morning do not begin thinking about the day ahead and do not switch on your smartphone before doing these three activities.
You will find relief within a few days when you practice the above consistently. Since doing these activities would need you to either watch the video or listen to the audio, I suggest you do so for a few times during the day until you are able to do it without these. Because you need to do it after switching off your phone.
The first activity is FGCB (Fixed Gazing and Conscious Breathing). This is explained in the article linked here. Selvan Srinivasan’s answer to What are some breathing exercises for beginners who struggle with focusing on their breath while meditating?
The second activity is Deep crossing. Watch the YouTube video to learn this. Selvans Deep crossing: https://youtu.be/qq6iKZquuVI
The third is Look, Breathe, Tap – eyes open meditation. Listen to this guided meditation audio to learn this. Selvans Guided Meditation – Look Breathe Tap
Once you are completely healed from this issue after a few days, if you are interested to learn more and go into deeper healing practices, please visit my website linked below.https://awarenessjourney.org/