Apparently you can, which is news to me, i imagine youd need a doctors confirmation that its relatively severe and not this self diagnosed nonsense some people try to pull these days. Either way, check the link and contact sfe or whoever disperses it as theyll be able to help you with any and all questions apropos the allowance. https://www.gov.uk/disabled-students-allowance-dsa/eligibility
Yes, you can. You will need to fill in a disability evidence form for student finance either from your GP or a suitable medical professional (psychiatrist). It is usually accepted as long as the evidence states that it is anticipated to last longer than 12 months, and the condition impacts your studies.