If u're not performing as expected, then

it's legal for yr super to do anything including giving u warning, getting pregnant cannot give u an excuse to avoid doing yr job, well, employer is usually careful since they don't want lawsuit, but if it's not a big company, or if it is as u stated (u fall into sleep during work), then he has every right to do so, sorry... to most u can say about him is he's not sympathetic enough, but he's not violating any laws!!!