Sleep requirements of a person vary with age. An adult may require 7-9 hours of sleep in a day whereas a toddler needs 11-14 hours of sleep. If your toddler sleeps about this much of hours, takes short naps and keeps waking at night, then its completely normal but if he sleeps more than usual, then it can be reasonable. Most of the times, the reason is growth spurt.
In times of growth spurts, toddlers usually take longer naps than usual and collectively longer sleeping hours. Another important reason can be the bout of teething. It makes your toddler irritable often. During teething, toddlers tend to take shortened naps and keep waking at night, due to which they aren't able to get sound sleep. Sometimes, babies even get a mild fever. All these things make a baby feel lousy and sleepy. Last but an important reason can be an illness. For instance, during cold, a toddler keeps waking at night due to discomfort and the naps also get short. Your baby needs more rest and energy to fight off the infection. Therefore, they feel extra sleepy and lousy too.