What constitutes a hostile work environment?

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Your question is pretty complicated - as evaluating whether a "hostile work environment" is actionable requires a thorough evaluation of the "totality of the circumstances" surrounding the employment.  If any of your manager's "serious control issues," as they relate to you, are motivated in any way by a category protected by the California Fair Employment & Housing Act, or any other anti-discrimination provision in California or federal law, then you may have a case. 

Among other protected categories, an employer is forbidden from discriminating against an employee on the basis of a disability.  Similarly, an employer and its employees are forbidden from harassing another employee on the basis of a disability.  If you believe that you were harassed and/or an adverse action was taken against you because you have a disability, you may have a case and should consult an attorney.

Additionally, you mention that you are currently out on a leave.  If your leave qualifies under either the FMLA and/or the CFRA, then generally, an employer has to reinstate you to the same position that you held at the start of the leave (or a similar position).  Additionally, if your leave qualifies under either the FMLA and/or the CFRA, then an employer cannot retaliate against you for taken a leave.  If you believe that either of these has happened, you should consult with an attorney.

There are also other leaves and laws that may apply to your circumstance, but from your brief description, I cannot tell if they apply.

Unfortunately, there is no right whatsoever to a pleasant, professional, respectful, comforatable workplace, and coworkers and employers are allowed to be insulting, unplesant, etc. If you have an employment contract, your rights to employment as contained in that contract may be enforced. If not, and if you believe that you are being discriminated against or harassed owing to a protecting category, such as your race, religion, sex, age over 40, or a disability, you may have a workplace discrimination claim. Other than that, your supervisor and coworkers may legally be as nasty as they like, and you choice is whether to put up with it or seek other employment. (Note: they may not commit defamation, which is the public making of untrue factual statements that put you in a bad light or damage your reputation--be aware though that opinion statements are allowed.)