First of all, noone here can know what is really the matter with you. So we all find it rather alarming, because
"Not getting yourself to do exciting things" can be a symptom of serious medical problems.
However, after a "work-sprint" you may just be exhausted in a perfectly normal way. E.g. after I had handed in my Diplom thesis, I needed two weeks of basically doing nothing and sleeping a lot (incidentally and very typically, I got a cold as well). It's just paying back your debts in recreation, in the very literal meaning of the work.
Things to do:
Talk to your advisor. From what you wrote, you have a very good relationship. If you think you are in the normal need-for-holidays, tell him, and get the holidays.
During the holidays,
Sleep much
Spend much time outdoors. Sun (in case it's winter now where you are) and excercise is good for everyone and you may need to catch up due to the work sprint. Doesn't need to be real sports, for me personally it would be better to do "excercise" on a non-exhausting level, but longer. 5 - 8 h of walking, biking or slow cross country skiing would sound good to me, but your marks may vary of course. I'd say, a good amount of fresh air is when you fall into your bed at 8 pm and sleep till next morning...
Make sure you eat lots of vitamins
If you are afraid (i.e. you are not 100% sure that it isn't) something more serious may be the matter:
Don't wait until you know it is serious! By then, it will be very serious, and you may not be able any longer to seek the help you need.
Also talk to your advisor. If you think, holidays may help, take them. However, here are two additional "saftety lines":
- Schedule a meeting for after your holidays to discuss whether you are again in working condition. Ask him now that he should get you to medical help if you are not in working condition after the holidays.
- Ask him to come and get you to medical help if you don't show up after holidays.
In addition (before the holidays),
find out whether your university has some kind of psychological counselling (not sure about the correct English name), examination offices usually know that.
Alternatively, find out a psychological clinic (university hospital?) with emergency counselling hours (again, someone please correct my English)
If you don't get yourself to doing this now (till Monday noon), go to your advisor (or very good friends/relatives), tell them you have a psychological emergency and that they should get you to medical help immediately.
Normal exhaustion after intense work:
Personally, I know and love these exciting periods of intense work. However, they are exhausting, and you need the recreation afterwards as you'd recreation after a mountain tour of several weeks. Also, they don't happen every day (I think one couldn't survive that, even though they are incredibly good). BUt from what I know from fellow researchers, these a serious driving force for quite some of us. Welcome!
Even though you are now exhausted, remember how good it is. I think a healthy balance is if you are exhausted like you are exhausted after a big physical effort. I remember them like physically strenuous tours.
They are not an every-day experience, but odds are that this wasn't the last experience of the sort :-) And, while this one may have been too much of the good, you can learn knowing when it is enough (and/or to plan for recreation afterwards). For me, this got easier once I had the experience that new such spells of incredibly good work do come.