If you type /suicide into your chat window, you will swallow your own tongue and die. You will have the normal respawn options as with a normal death. This is useful if you get stuck somewhere or get lost after exploring.
Will result in normal death skill loss, which is 0.25 from a few skills and 0.01 body strength. You will still lose full skill if you /suicide on a deed. To lose less skill on a deed, you must die via normal means, such as attacking the guards present.
Keep in mind however, suiciding will still leave a corpse at the spot you died containing all the items you had in your inventory, except for non-drop items (e.g. deeds, writs, etc), which will stay in you inventory when you respawn.
It appears there is a 5 minute cool-down timer between /suicides.