MYSQL error 2006 when running an UPDATE based

[ELMANDOUH MAHMOUD]

get mysql error 2006 (server gone away) when trying to run the following SQL query:

UPDATE user_items
SET A = A + 1, B = B + 1
WHERE uid IN
(SELECT uid FROM user_achievements WHERE C >= 10)
I've heard that error 2006 happens when the queries are very heavy.

Would like some advice on how I could either the optimize the above query or bypass the error?

My database is running on MySQL 5.6.

Thanks.