For the past week and a half I've been having the feeling that my heart is beating stronger than usual for no reason, and there's also a feeling of pressure between beats sometimes, like its doing one very strong beat between the strong ones. The feeling comes and goes, and is more noticeable later in the day than it is in the morning.

I have recently been switched from Seretide to Symbicort for my Asthma, I used the old Seretide again a few times due to it being close to hand (before the problem started), and then when the problem started I switched myself back to Seretide fully, but the problem is still here after like 4 or 5 days.

Is there a drug iteration going on? for the time being should I be using Seretide, Symbicort, or making do with Ventolin?

Or is something else going on? I mean I've been using only Seretide for the past 4 or 5 days, and it never caused me problems before, surely the Symbicort would not be still in my system enough to interact by now?