She cannot move her head because of severe pain; how should she pray?
Question

                A sister is asking that she has a very strong pain in her head that makes her vomit. When this happens she cannot pray in any position, as she cannot raise her head. How shall she pray when prayer time comes?.
Praise be to Allah.Firstly: 
We ask Allaah to grant our 
    sister healing and well being in her religious and worldly affairs. 
Secondly: 
If the time for prayer 
    comes and she feels pain, then she may delay the prayer until the end of its 
    preferred time, in the hope that she may be able to offer the prayer in the 
    proper manner. But if the pain persists, then she may pray in the manner 
    that she is able to, even if she is lying on her back. 
The basic principle 
    concerning that is the verse in which Allaah says (interpretation of the 
    meaning):  
“Allaah burdens not a 
    person beyond his scope”
[al-Baqarah 2:286]. 
And the Prophet  (peace 
    and blessings of Allaah be upon him) said to ‘Imraan ibn Husayn: “Pray 
    standing, and if you cannot, then sitting, and if you cannot, then (lying) 
    on your side.” Narrated by al-Bukhaari (1117) and Abu Dawood (952). 
If a person prays sitting, 
    then he should lean forward for rukoo’ (bowing) and sujood (prostration), 
    and he should lean forward more for prostration than for bowing. 
If a person prays lying on 
    his right or left side, then he should tilt his head towards his chest for 
    bowing and prostration.  If a person prays lying on his back, he should put 
    his feet towards the qiblah and tilt his head towards his chest for bowing 
    and prostration. If he is unable – when sitting or lying – to move his head, 
    then the actions are waived in his case, because that is the thing that he 
    is unable to do, but the words are not waived because he is able to say 
    them, and Allaah says (interpretation of the meaning): “So keep your duty 
    to Allaah and fear Him as much as you can” [al-Taghaabun 64:16]. 
    So he should say takbeer and recite Qur’aan, and intend to bow and say 
    takbeer and recite the tasbeeh of bowing, then he should intend to stand up 
    and say Sami’a Allaahu liman hamidah, rabbana wa laka’l-hamd 
    (Allaah hears the one who praises Him, our Lord to You be praise) etc. Then 
    he should intend to prostrate and say takbeer and the tasbeeh of 
    prostration, because this is what is implied by the shar’i principle, “So 
    keep your duty to Allaah and fear Him as much as you can”. 
End quote from al-Sharh 
    al-Mumti’ (4/332). 
And Allaah knows best.