Sleeping in Sukkah:[1]

It is forbidden to sleep outside of a Sukkah even a mere nap.[2] If one feels cold in the Sukkah, due to the cold weather and lack of blankets, then he is not obligated to sleep in the Sukkah. Furthermore if one is unable to set up his sleeping quarters in the Sukkah without needing to remove the furniture from the Sukkah during meal times, in a  way that he would not trouble to do so in his house, then he is exempt from sleeping in his Sukkah.[3] Today the custom of the world is not to sleep in the Sukkah with exception to those which are very particular in Mitzvos. Some have defended their practice based on the fact that one is obligated to rejoice his wife during the festival and since the wife does not sleep in the Sukkah they sleep with the wife in the house, and hence since one is involved in one Mitzvah he is exempt from another Mitzvah. Nevertheless it is proper to be stringent to build a Sukkah in a way that one can sleep there together with his wife and hence fulfill both Mitzvahs.[4] [The Chabad practice is not to sleep in the Sukkah due to that one is unable to be conscious of the holiness of the Sukkah during sleep, and this causes one pain, and anyone who is in pain upon dwelling in the Sukkah is exempt from the Mitzvah.[5]]

 

Summary:

One may sleep outside his Sukkah if either:

1. It is too cold and does not have warm enough blankets
2. One does not have enough room to store his bed there together with the table
3. His wife desires him to sleep with her in the same room

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[1] 639/7

[2] The reason: Now although it is permitted to eat a mere snack outside the Sukkah and only a set meal is forbidden, nevertheless since a nap can power and reenergize a person just like a regular sleep therefore it is considered like a complete sleep and is forbidden to be done outside a Sukkah. [ibid]

Other opinions: Some Poskim write one may sleep up to 100 Ama worth outside the Sukkah. This is approximately 54 seconds. [See 639/2; Piskeiy Teshuvos 639/6]

[3] 639/8

If one is troubled by the necessity to remove the table and enter the mattress and blankets and then reenter the table during the time of the meals, then if one would not trouble himself this amount to sleep in his house he is exempt from sleeping in the Sukkahm as everyone who has pain from dwelling in a Sukkah is exempt from the Mitzvah. [ibid]

[4] 639/9

[5] See Appendix