All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad, sallallaahu 'alayhi wa sallam, is His slave and Messenger.
What the questioner mentioned in his question might be due to his own actions because some people act in the state of sleep as they would when awake. They may sit, stand, walk and move about without realizing it especially, if they go to sleep very tired.
On the other hand, it could be the work of Satan since he is keen on stopping Muslims from worshipping Allah and making them miss every opportunity to do so. The Prophet said: “Satan puts three knots at the back of the head of any of you if he is asleep. On every knot he reads and exhales the following words, “the night is long, so stay asleep”… [Bukhari and Muslim]
Allah Says (what means): {Shaitan (Satan) wants only to excite enmity and hatred between you with intoxicants (alcoholic drinks) and gambling, and hinder you from the remembrance of Allah and from As-Salat (the prayer). So, will you not then abstain?} [Quran 5: 91].
As long as you try your best to wake up for Fajar prayer and make every effort not to miss the prayer then if those things which you mentioned in your question, either from yourself unintentionally or Satan, we hope Allah will forgive you, and reward you for your intention and efforts to make the Fajar prayer.
Allah knows best.