The usage notes in the wiktionary entry for condescend point out that
• This is a catenative verb that takes the to infinitive. See Appendix:English catenative verbs
• In sense “to talk down”, the derived participial adjective condescending (and corresponding adverb condescendingly) are more common than the verb itself.
The appendix linked to in the above quote explains the term catenative verbs at more length:
Catenative verbs are verbs which can be followed directly by another verb — variously in the to-infinitive, bare infinitive or present participle/gerund forms. For example He deserves to win the cup, where deserve is a catenative verb which can be followed directly by another verb, in this case in the to-infinitive form.
Most of these verbs demand that the following verb be in one or the other form only. A few can take both forms, but sometimes there is a difference in meaning.
They are called catenative from their ability to form chains. We promised to agree to try practicing playing tennis more often.
Note, the sense “to talk down”, mentioned in the first quote, refers to sense 2 of condescend:
To treat (someone) as though inferior; to be patronizing (toward someone); to talk down (to someone) [eg]
1861, Charles Dickens, Great Expectations, ch. 29:
"You must know," said Estella, condescending to me as a brilliant and beautiful woman might, "that I have no heart."
1880, Charlotte M. Yonge, Clever Woman of the Family, ch. 7:
Ermine never let any one be condescending to her, and conducted the conversation with her usual graceful good breeding.
In short, “Don't condescend me” is incorrect; I've never heard anyone say it, and have never seen it written before. I doubt that it is commonly heard anywhere among native speakers.