It would depend on the uni and the course. Your best bet is to contact your former Course Leader and ask. You may be able to restart the course if you've left in first term, or restart the year next September if you're further through. It would be entirely up to the uni and each case will be decided on its individual merits, so there's no way anyone here can give you a definitive answer.
Do be sure that the reasons you withdrew, have been resolved and will not recur. You don't want to put your health at risk by rushing back to uni, when maybe a break from studying would be better for you.
Check the Student Finance situation though. You get one "grace" year of funding, so if this was your first term you should be able to restart from your first year and still get your full entitlement.