Brief Answer:
Ulnar neuropathy.

Detailed Answer:
I read your your query carefully and I understand you concern.

By your description of the symptoms seems like a typical case of ulnar neuropathy, meaning irritation of the ulnar nerve which covers the area where you feel the symptoms.

That usually is related to irritation of the nerve in the elbow or less often in the wrist. Often that is caused by trauma in that area, so if you recall a recent hit or injury that might be the cause.
Also it has often been related to professions which include repetitive flexion and extension of the elbow, or leaning with the inner part of your elbow on a table for a long time, bending the elbow for long stretches of time, repetitive wrist movements and so on.

The diagnosis should be confirmed by electromyography (EMG) and nerve conduction studies which will also precise the area of irritation and degree of damage.

It is no reason for panic, if the predisposing factor is removed it could improve (gradually not overnight) by itself. Treatment includes pain-killers (if in pain), oral Vitamin B6 supplements, physical therapy, carrying an elbow pad or night splinting. If persistent surgery could be considered.

I remain at your disposal for further questions.

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Brief Answer:
Not likely for that particular position.

Detailed Answer:
That is a good question.

As I said any action straining or compressing your elbow or wrist could predispose it to happen, so a prolonged unconscious compression due to certain positions during sleep is possible.

That being said that particular position you mention, with the arm over the head, shouldn't have any influence as it doesn't put any pressure or stretches the nerve.

I hope to have answered your question (If you do not have any other question, you can close the discussion and rate the answer).
Wish you good health.

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