Berachos, Chapter 2, Mishnah 6. Continuing the theme that emerged in the previous mishnah, that Rabban Gamliel would at times conduct himself differently from the accepted halachah, the mishnah now tells us about his conduct during his period of mourning.
An incident with Rabban Gamliel:
When Rabban Gamliel's wife passed away, he washed himself already on the first night after her passing - this despite the fact that he was a mourner, and despite the fact that a mourner is generally forbidden to wash.
The students' objection and his answer:
His students said to him: "Rabbi, lo limadtanu she'avel asur lirchotz?" - "Our teacher, did you not teach us that a mourner is forbidden to wash?" He answered them: "Eini k'she'ar kol adam, istenis ani" - "I am not like everyone else, I am delicate." For him, washing was not a form of pleasure, as it is for other people, but a genuine need, since he was simply unable to manage without it.
In summary: In this mishnah we learned about Rabban Gamliel's conduct, that he washed on the first night of his mourning, and about his answer to his students - that he was delicate, and therefore washing was not for him a pleasure forbidden to a mourner, but a need for which there was no substitute.
In practice, regarding the question of how a mourner should actually conduct himself, one should turn to the local Orthodox rabbi and ask for a practical ruling.