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You answer your own question. There is a fall in temperature because the reaction is endothermic. The reaction needs energy, so unless you can supply some heat, the temperature will fall. Eventually, some heat from the surroundings will transfer and equilibrate the temperature. Temperature of the system is a measure of the global energy. Most reactions are exothermic so now the temperature rises and then transfers to the surroundings. A very famous example is a burning fire.
These are reactions that take in energy from the surroundings. 1  The energy is usually transferred as heat energy, causing the reaction mixture and its surroundings to get colder. The temperature decrease can also be detected using a thermometer. Some examples of endothermic reactions are: 2  electrolysis.