Did something like this happen before
No. Definitely not.
some random questions and texts appeared I never selected
Could you please post the URL of your questionnaire? When did that change occur? Are we talking about text that you have never written? Do you have an example?
Please also check if you have multiple questionnaires under Compose Questionnaire.
can I get my old questionnaire back or do I have to compose it again?
Hard to say... Let's first find out what happend.