It could be something as simple as requesting a quiet workspace. Or it could be something as significant as asking to have a new desk that accommodates your wheelchair. If it is reasonable and does not constitute an "undue hardship" on the part of your employer, your disability request must be provided.
What is considered a disability?
The Americans with Disabilities (ADA) act was signed into law in July 1990. The act created a requirement that your employer make changes to your work environment that allow you to work. According to the U.S. Office of Personnel Management, the following is required for any employer with a disabled employed:
"Reasonable accommodation is any change to a job, the work environment, or the way things are usually done that allows an individual with a disability to apply for a job, perform job functions, or enjoy equal access to benefits available to other individuals in the workplace."
What does that mean for you?
In a nutshell, if you have a disability--whether obvious or not obvious--you may request accommodations so that you are able to perform your job and enjoy the benefits offered to the other employees.
There are many kinds of disabilities--it could be something such as having a hearing or sight impairment, or it could be a mental health diagnosis such as PTSD or Autism. If there are ways your employer can make your workspace comfortable for you so that you can thrive at your job, your employer is required to do so.
Must they provide anything I request?
Bear in mind though, that not every request may be granted. If your request is to work from home, but your job requires that you drive a fork-lift, it's obvious that that request would be a hardship for your employer. Similarly, if you request that you be able to nap everyday due to an illness, this request might be granted, but the employer is not required to pay you for the time you spend asleep.
Most employers are eager to accommodate their employees. So, be sure you are asking for the help you need to perform your job to the best of your ability. If you feel your employer is not willing to accommodate you, have a conversation with an ADA attorney.