While singlehanders are forced to sleep with no one on watch, it does violate the colregs and should be avoided if possible. If you are single-handing and are left with no choice, you would want to make sure that you are:
1. Out at sea and well away from any reefs
, shallows and land masses;
2. Out of the shipping
3. Have radar
with an alarm
to awaken you in the case of approaching vessels.
4. Have an autopilot
with an interface to your wind-direction instruments - compass
courses are of little or no use on a sailboat in shifting winds.
It also helps to be a light sleeper. Most of us will awaken at anchor
, or underway when there is any significant change in wind/wave direction and intensity.
You can use a stand alone weather
fax, or your computer to obtain weather forecasts/sat photos while underway. For the latter you will need a Ham Radio
with an appropriate modem
If you haven't sailed, I would suggest that you join a yacht club and try to get some time crewing
night. There are also cruising courses available in the USA, the caribbean
and the med (and no doubt elsewhere).