Emails disappeared overnight from my Apple Email on iPhone and iPad

This morning I looked at my Apple email inbox on my iPhone 11 and all emails since last Saturday have disappeared - there were quite a few and it’s very frustrating. The same thing on my iPad and also the web based iCloud webpage. Where have they gone, can I get them back and why did this happen suddenly? I haven’t had any problems previously and now I’ve lost confidence in the email system. Is anyone able to help, please?