Tomcat Mysql connection hangs after about 30 minutes

Question

Facts:

• 1 Tomcat installation , 1 MySql and 2 applications ( app1 and app2 )
• Hosted on shared hosting, so most of admin stuff with mysql is not possible

• When tomcat is started the applications ( both app1 and app2 ) are working fine

• After about 30 minutes... I try to log in my app1

• Sometimes it logs in and sometimes it just sits there and kind of "hangs"

• Even if I log in.... after a click or a few clicks it stops responding ( like above )

• If I check in phpMyAdmin, there are some processes in "sleep" mode

• killing these will not solve anything
• If I check in Tomcat Manager...there are these process sitting there as well

My analysis :

• There are no permanent connections or connection leaks ( already checked )
• Tomcat is up ( since manager is responding well )
• MySql is also up ( since I am able to see the processes and kill them too )...and run queries
• I guess there is some connection problem between Tomcat and Mysql
• Something like Tomcat is sending and Mysql is getting but not replying back

My Doubts :

• What could be a thing which is causing this ( timeout ? )
• It HAS to be something which is ok at the start but goes wrong after 30 minutes or so

Please help. ( Tomcat logs are not very helpful. Though I have struts log from log4j )

thanks, Mayank