Your ds is showing some signs of what is called in spanish "Golpe de Calor"
sorry i don't know the name in English, the literal translation would be Heat Beat or something like it. Basically on summer time (specially this past few years where heat has been awful) kids and elder people might appear letargic and dizzy, throwing up and being upset but not fussy. Symptoms are not related to heat cause the don't appear sweaty but that's the tricky part: body gets so heated up because it is keeping all the warmth from the outside, that is unable to sweat anymore and just gets heated and heated without a chance to release it. The prescription is usually try to keep them as cool as possible, even if you have to spray them with water from an athomizer every once in a while, tons of water and keep diet very low key (just boiled chicken, very few "hard" vegetables as peas and carrots, not the soft type as aesparragus or potatos, grains like rice or pasta are ok but cereal is better to be kept on held) and visit your doctor if he looks feverish.
Another thing could be a stomach bug, which is also pretty common during heat times, cause meals tend to spoil sooner because of high temperatures.
Anyways, Im in no way a health specialist, i just wanted to point out that i think his sleep issues are more caused by a combo of heat/illness in development than the molars, cause he's too young for the 2 year molars, besides you can't see the other symptoms as the itchy gums etc. The Calpol might have worked because he was feverish and that helped his temperature to go down. Keep an eye on him, take his temperature as often as you can, keep his room EXTRa fresh and keep him hydrated (here in Mexico, giving milk and other beverages straight from the fridge is adviced, I don't know if you're comfortable with it).
Along with it, you could try posting in the Health/Medical needs for further advice and call your ped to see if he has more insights on this.
Good luck! and I hope lo gets back to his old self real soon!