Is your Swedish ID card the same kind of ID card that is issued to Swedish nationals? According to what I have read a national ID card (which doubles up as a passport for travel within the EU) is only available to Swedish citizens. If your identity card is of the "certified identification card" type referred to in my earlier post then Ryanair will not recognise it as a valid travel document.

Ryanair have recently changed the rules on what documents they will accept. They will no longer accept ANYTHING except (a) passports and (b) identity cards of the type that can be used instead of passports to cross non-Schengen borders within the EU. It doesn't matter whether you are flying nationally or internationally with Ryanair, you will NOT be allowed to travel unless you can produce a passport or a government-issued identity card that is formally recognised as a travel document for intra-EU travel. A residence card issue to a foreign national is NOT a formal travel document.

As an aside British nationals now need to carry their passports to take Ryanair flights within the UK, no other documents are accepted any more (there are no identity cards in the UK). Not a government rule, just a Ryanair rule. All other airlines accept driving licences and other photo ID documents, Ryanair insists on a passport.

Will Ryanair check your visa? You don't say what your nationality is, but if you are of a nationality that requires a visa for Schengen then yes, definitely. If you're a non-visa national they may not look quite as closely.

I wouldn't take the risk if I were you. Just get a train.