I'm unable to view my emails as usual unless I double click or tap twice on the touchpad, why is this happening?

Initially when I tap once on my email or message in mail, I could see and read the entire content, but lately starting from 2 days back I can't seem to read my mails anymore unless I double click or tap twice on the mail. I believe something is wrong but can't seem to figure it out why this is happening because the mail also seems to be somewhat slow and appears to be flickering in the minimized display. Can someone please help me out??