Do you smoke, drink, eat gluten and sugar? Is your back in alignment? Are you sleeping in a weird position?
There are so many things that affect circulation. If it continues, start seeking reasons you have inflammation in your body, reasons your circulation might be limited, and work on them one by one.
I had a "dead" hand a lot this summer and massage and regular hot soaking helped a lot. Of course, sitting in a cramped little boat is part of it, but I've paddled with a lot of boaters that have to get out and shake their feet every 20 minutes and many who haven't. Find out what works for you - pins and needles sucks!