Can you suddenly turn into a sleep walker?

Yes. Sleep walking has genetic predisposition but is also sensitive to triggering factors, such as sleep deprivation / tired. Since having brand new sleep walking in adulthood is less common, it will be good idea to see a doctor to make sure your new sleep walking is not caused by seizure disorder or medication.
That can happen. Sleep walking is more common in children. It is also more common under stress. Some medications such as Ambien (zolpidem) can precipitate sudden bouts of sleep walking and eating. Generally sleep walkers do not hurt themselves but they can. Sleepwalking in children dissipates in adolescence usually. Sleep talking is also common in children. Random sudden sleepwalking in adults is rare.