It's very normal for babies to suddenly cry throughout the night during the first 6 months of life.
After 6 months of age the crying in the baby slows down and the baby will not cry as much.
However another thing happens when babies reach 6 months of age which is separation anxiety which can cause the 6 month old or older baby to start crying at night because they want to be near you or want to be held.
Sometimes just getting near the baby or holding them in your arms and rocking them back to sleep can help with the crying.
The baby could also be in need of a diaper change or want some formula or they could be sick with a cold or flu or other illness.
Usually the sudden crying in the baby is nothing to worry about but you should always check on your baby if they do cry.
Babies are wonderful but they require you to have some sleepless nights and require a lot of work and are a big commitment.