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The pain can follow many different patterns, and it is frequently unknown why pain occurs at certain times and not others. Sometimes it may be related to certain positions or activities, but in many situations, the reason for pain at certain times cannot be determined.
This is not unique to radiculopathies. Pain can be better or worse at various times for most chronic conditions that cause pain.
It is true that distractions can make any symptom less noticeable, but this is usually apparent when that person has a quiet day, such on weekends or days off, and the symptom is as noticeable on those days as at night.
If the reason that the pain is not bothering you during the day is distraction, then it would be noticeable on quiet days.
Then the original answer applies.
That is something that would need the assessment of your doctor.
I knew you were changing medicines.
It is good that it is kicking in.
If this is bothersome, then you would need to talk with your doctor, but if the symptoms are mild, then they may ease as your body gets accustomed to the medicine.
If you developed a new symptom only after taking the lithium, it is suspicious for being due to the lithium.
I answered this in the other thread.