I have been wounded like this since about half past eight this morning and I will tell you how it happened. I had been feeling ill since the feast of the Magdalene [22 July] and had not been out on account of my illness except on Saturday and Sunday when I went to S. Giovanni [dei Fiorentini] for the Jubilee. Last night the idea came to me of making my will and writing it out with my own hand, and I began to write it about an hour after supper and I went on writing with a pencil till about three in the morning. Messer Francesco Massari my young servant ... who sleeps in the room next door to look after me and had already gone to bed, seeing that I was still writing and had not put out the light, called to me, 'Signor Cavaliere, you ought to put out the light and go to sleep because it is late and the doctor wants you to sleep.' I replied that I should have to light the lamp again when I woke up and he answered: 'Put it out because I'll light it again when you wake up'; and so I stopped writing, put away the paper on which I had written a little and the pencil with which I was writing, put out the light and went to sleep. About five or six I woke up and called to Francesco and told him to light the lamp, and he answered: 'Signor, no'. And hearing this reply I suddenly became impatient and began to wonder how I could do myself some bodily harm, as Francesco had refused to give me a light; and I remained in that state till about half past eight, when I remembered that I had a sword in the room at the head of the bed, hanging among the consecrated candles, and, my impatience at not having a light growing greater, in despair I took the sword and pulling it out of the scabbard leant the hilt on the bed and put the point to my side and then fell on it with such force that it ran into my body, from one side to the other, and in falling on the sword I fell on to the floor with the sword run through my body and because of my wound I began to scream, and so Francesco ran in and opened the window, through which light was coming, and found me lying on the floor, and he with others whom he had called pulled the sword out of my side and put me on the bed; and this is how I came to be wounded.
(taken from Anthony Blunt, Borromini, pp. 208-209.)
Francesco Borromini would die as a result of his self inflicted wound. He was buried in S. Giovanni dei Fiorentini, as the brothers at San Carlino (where he had wished to be buried and had spent much of his life as the architect) would not permit a suicide to be buried in their church.