yes I did name them unfortunately

Hi guys, I was looking round for advice regarding my hearing next week and stumbled across this site and thought you may be able to help. The situation is I have a hearing next week for a charge of gross misconduct and wanted your opinion on what would be a reasonable outcome. The charge is that I mentioned my employers on twitter after I returned home from work to find on my payslip I had been underpaid. I emailed HR and they said they still had my down as being off sick (I should explain at this point I have just returned to work after 3 months off with depression). I was obviously upset and made a very stupid comment on twitter (on which I wrongly assumed my tweets were still protected, no excusing it but a point I still want known). After being informed that I was being charged there was a short investigation meeting in which I admitted I made the comment and pointed out I was not at work while I made the post (which they assumed I was, but I am currently on a phased return). The rule about derogatory statements about the company over social networking sites was briefed out to employees while I was away from work and while I know it was stupid and wrong, I never knew it constituted gross misconduct. They have provided me with evidence collated from the investigation such as policies I have previously signed (with no reference to social networking), screenshots of my twitter account and with it they have a read receipt from myself for an email sent in May that I read on 13th July which contained the latest company policies. The issue with that was that the email contained links to the latest policies, not the policies themselves. The 13th July was my first day back in work and due to my account being suspended due to inactivity, could not access my email until 11am at which time I had 650 unread emails. I was due to finish at midday and as you can appreciate being off for so long, I wanted to get through them as quick as possible so the next day I could start doing some actual work and get myself back 'in the groove' of things and couldn't look through every email I received. Now yes, what they are accusing me of doing, I hold my hands up and say I did it. It was done out of anger and stupidity rather than malice or through any agenda against the company. The post never accused any individual of any wrongdoing or criminal activity, or indeed the company. I have never had disciplinary action taken against me before (and trust me, after this, never again). Honestly, where do I stand, would dismissal in this case really be a fair decision? Thanks in advance Edit: Should also point out that I have been suspended on full pay pending the hearing, shows that dismissal is what they're obviously pushing for