He suffers from laughing too much
There can be no doubt that laughing too much has an effect on the Muslim’s heart and distracts him from thinking deeply and fearing Allaah. The Messenger (peace and blessings of Allaah be upon him) warned us against laughing too much, and told us of the danger it poses to the heart when he said: “Do not laugh too much, for laughing deadens the heart.” Narrated by al-Tirmidhi, 2305; Ibn Maajah, 4193.
However, there is no specific du’aa’ that has been narrated for dealing with this particular problem. Rather you can call upon Allaah in whatever words you wish and ask Him, for He is the All-Hearing and Ever-Responsive, to relieve you of this problem and to give you a heart that is humble before Him and a tongue that remembers Him and an eye that weeps with fear of Him.
You should also read Qur’aan a great deal and ponder its meanings, and remember Allaah a great deal, make du’aa’ and turn to Him in all your affairs.
With regard to the sickness that you mention, we ask Allaah to heal you from it. It was the practice of the Prophet (peace and blessings of Allaah be upon him), if he suffered some complaint, to recite verses seeking refuge with Allaah over himself and then spit drily. This was narrated by al-Bukhari (4728) and Muslim (5679). It is also Sunnah for the sick person to put his hand on the part of his body that is suffering pain and say “Bismillaah (in the name of Allaah)” three times, then to say seven times: “A’oodhu Billaahi wa qudratihi min sharri ma ajidu wa uhaadhir (I seek refuge in Allaah and His power from the evil of what I feel and what I fear).” Narrated by Muslim, 5701.
Finally I wish to point out to you that going to doctors and taking medicine does not conflict with believing in Allaah and putting your trust in Him. Rather perfect trust in Allaah means availing oneself of the physical or material means as well as having complete faith that healing comes from Allaah, and that there is no healing except His healing.
We ask Allaah the Almighty, Lord of the Mighty Throne, to heal you and all the Muslims who are sick.