What is the worst situation in which I could find myself in the case my patent is very similar or identical to another, without doing it intentionally?
Can I be sued from the other inventor, or can I just lose my patent's ownership?
I agree with OutputLogic that a second patent application filing that is "very similar or identical to another" previously filed patent application should not ultimately issue as a patent; however, it is not uncommon for unrelated inventors pursuing solutions addressing similar technological issues to have patent applications with similar disclosures proceed through the USPTO concurrently without Examiners becoming aware of the conflict. This can happen when the different inventive groups use different terminology in their patent applications, for example.
Depending upon the timing of the two patent applications at issue or the issuance of one patent relative to the filing date of the other patent, your patent might become the subject of an interference proceeding, a derivation proceeding and/or a post grant review proceeding (e.g., an ex parte reexamination or an inter partes review), but you are not going to be "sued" for the mere existence of an issued patent having a similar disclosure to another patent - unless the other party has reason to believe you did something improper, e.g., misappropriated or used improper means to discover a trade secret of theirs, breached a confidentiality agreement or the like.