Locate  the  difficulty  files in your Crysis installation folder
(ie: C:\Program Files\Electronic Arts\Crytek\Crysis\Game\Config).
These files  are called diff_easy.cfg, diff_normal.cfg, diff_hard.cfg
and diff_bauer.cfg. Open the file (with Notepad) that corresponds to
the difficulty level you are playing. Add the following line to the
end of the file and save it:

g_godMode = 1 

Now, when playing  your health will still decrease but you will
not die. Instead, your health and armor will automatically replenish
when your health reaches 0.