K.B.
Could be night terrors, they tend to start around this age (not all kids get them). Eventually they get few and far inbetween (my daughter is almost 4 and rarely has them, maybe once a month to ever three month).
You are not to wake them up, do not turn on lights, make sure there is nothing around them that can hurt them. You can ask if they want you to pick them up and if they answer yes do it gently and hold & rock them gently. Or you can just say, mommy & daddy are here, and stroke her head or back. Sometimes my daughter will talk with me and I try to reassure her that I am here for her, she sometimes tells me what she is dreaming/doing and I can help talk her through it. Sometimes they are done in 2 mins others can last 30 mins. Sleep walking can also happen, and once again if it does do not wake them and keep them safe (I stand by our stairs and she usually comes toward them but bumps into me and I just gently turn her around and she walks somewhere else).
Lack of sleep seems to really trigger them in my daughter so I try extra hard to make sure she has all the sleep she needs to have a peaceful rest.