Here's an alternative:

SELECT u.*, n.ID, n.notes

FROM UserTable u

INNER JOIN Notes n ON

(u.lastaccounttype = 'account1' AND n.account1 = 1) OR

(u.lastaccounttype = 'account2' AND n.account2 = 1) OR

(u.lastaccounttype = 'account3' AND n.account3 = 1) OR

(u.lastaccounttype = 'account4' AND n.account4 = 1) OR

(u.lastaccounttype = 'account5' AND n.account5 = 1)

Edit: Added the sql and /code tags around the SQL.