Your pension fund remains invested in drawdown while you take an income from it. With flexi-access drawdown you are able to take as much income from your pension fund as you wish. You can choose to take regular payments monthly, quarterly, bi-annually or annually, or you can take one-off payments if you prefer. Although if you withdraw large amounts you should consider that this might result in you paying more tax. If you are reliant on the income from your pension to support you, you should consider taking a level of income that is sustainable for your lifetime.
If you started your drawdown pension before 6 April 2015 you may be in 'capped drawdown'. If you are in capped drawdown you may be able to contribute more into your SIPP than if you flexibly access your pension. You should consider whether the amount you can pay into your pension is important before deciding to convert to flexi-access drawdown to take income without any limits.