The Texas legislature has consistently made it harder and harder for citizens to "clear" their record of criminal charges. It sounds as if you entered a plea of guilty and were sentenced. If your sentence resulted in either a probated sentence or a regular sentence of either jail or prison time, then you would not be able to receive an expunction. If the agreement resulted in a deferred adjudication, you may be able to have those records nondisclosed, but when that can occur will depend on whether it was a felony or misdemeanor adjudication.
I agree somewhat with Mr. Hugger. Actually, the law that allows one to seal their record (non-disclosure) is only about 3 years old. If you served out a felony deferred, then when the statute of limitations has run, you can ask the trial court in which your case was prosecuted to seal the record. Most, at least in Houston, will if you have not been in other trouble.
There is a difference between been manic or otherwise suffering from a mental health issue and being insane. As you probably are aware from media cases, it is very, very difficult to be found insane. And, if you received advice to take a final conviction, it could be out of concern that you could not complete a probation because of your mental issues, and you would end up with a significantly greater prison sentence.
If you believe that you did not receive effective representation from your lawyer, consult a lawyer who handles post conviction applications for writ of habeas corpus. You may be able to get collateral relief in the form of a new trial, although it is very difficult.