Invocation (Dua'a) when you feel pain in your body

Put your hand on the place where you feel pain and say: Bismillaah. "With the Name of Allah' (three times).

Then say : 'A'oothu billaahi wa qudratihi min sharri maa 'ajidu wa 'uhaathiru. 'I seek refuge in Allah and in His Power from the evil of what I find and of what I guard against.'

[Reference: Muslim 4/1728. Fortress of the Muslim.]

Invocation(Duaa') in times of worry and grief

Allaahumma 'innee 'abduka, ibnu 'abdika, ibnu 'amatika, naasiyatee biyadika, maadhin fiyya hukmuka, 'adlun fiyya qadhaa'uka, 'as'aluka bikulli ismin huwa laka, sammayta bihi nafsaka, 'aw 'anzaltahu fee kitaabika, 'aw 'allamtahu 'ahadan min khalqika, 'awista'tharta bihi fee 'ilmil-ghaybi 'indaka, 'an taj'alal-Qur'aana rabee'a qalbee, wa noora sadree, wa jalaa'a huznee, wa thahaaba hammee.

'O Allah, I am Your slave and the son of Your male slave and the son of your female slave . My forehead is in Your Hand (i.e. you have control over me) . Your Judgment upon me is assured and Your Decree concerning me is just . I ask You by every Name that You have named Yourself with , revealed in Your Book , taught any one of Your creation or kept unto Yourself in the knowledge of the unseen that is with You , to make the Qur'an the spring of my heart, and the light of my chest, the banisher of my sadness and the reliever of my distress.'
[Reference: Ahmad 1/391, and Al-Albani graded it authentic. Fortress of the Muslim.]