Numbness, tingling, pain and weakness in the hand, particularly at night, may be caused by the nerves supplying the hand being compressed.
When the nerve supplying the thumb side of the hand (median nerve) is compressed as it passes into the hand this is known as Carpal tunnel syndrome. This can be managed with splints, steroid injections or surgery.
If the nerve supplying the little finger side of the hand is compressed around the elbow (ulnar nerve) this is known as
Cubital tunnel syndrome. This can be managed with splinting or with surgery.
Other causes of numbness can be neck conditions, problems with the blood supply, or damage to the nerve itself - for example from diabetes. This can usually be determined by a careful clinical assessment but sometimes nerve tests or a diagnostic injection will be recommended.
Image courtesy of Blausen.com staff (2014). "Medical gallery of Blausen Medical 2014". WikiJournal of Medicine 1 (2). DOI:10.15347/wjm/2014.010. ISSN 2002-4436. - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=27796924