Is one sinful if he misses Fajr prayer after waking up to the alarm, only to be overcome by sleep, knowing that he went to bed late and has never missed a prayer before?

If you wake up to the alarm after the prayer time has begun, you are not permitted to go back to sleep if you know or strongly believe that you will not wake up [again]. If you believe that you will wake up, then there is no sin upon you, but your sleep after the time has begun is disliked (makrooh). However, if you woke up before the time [for prayer] began, then there is no sin upon you in returning to sleep. You must make up this prayer, and if you were sinful, then seek Allah’s forgiveness and repent to Him.