My doctor prescribed me codeine 30mg x2 tablets every 4-6 hours. it seems to lower my heart rate below 60 bpm and i feel mildly breathless 5 hours later.are the side effects common and is there anything that can help relieve them whilst it wears off?

Those symptoms can be side effects of codeine but not common. You just stop codeine and its side effects will resolve.

We don't know the reason for the codeine.. A heart rate of 60 is not at all unusual for a healthy young person & it shouldn't cause breathlessness. If breathlessness occurs at rest but not with exertion, it tends to exclude cardiopulmonary causes & points toward anxiety. If all resolves off codeine, no worries. If not, see your MD for an evaluation.